阅读说明：本技术 一种钻井壁强化型岩气储层油基高温高密度钻井液 (Drilling wall reinforced rock gas reservoir oil-based high-temperature high-density drilling fluid ) 是由 杜征鸿 沈建文 睢圣 王兴忠 李衡 罗翰 张珍 陈仕仪 陈建君 陈虹霓 于 2021-08-09 设计创作，主要内容包括：本发明公开了一种钻井壁强化型岩气储层油基高温高密度钻井液,油基高温高密度钻井液原料组成重量份如下；油相：80～95份；主乳化剂：2～4份；辅乳化剂：2～4份；润湿剂：2～4份；有机土：0.5～3份；降滤失剂：2～6份；流型调节剂：0～3份；随钻承压封堵剂：2～8份；粒径可变复合封堵剂：1～4份；石灰：2～4份；超细碳酸钙：3～5份；25％CaCl2盐水：5～20份；API标准重晶石：加重至2.05～2.3g/cm3。该随钻井壁强化型页岩气储层油基高温高密度钻井液体系在高温条件下热稳定性强,钻井液流变性易于调控,随钻封堵性能强,且性能维护简单。(The invention discloses a drilling wall reinforced rock gas reservoir oil-based high-temperature high-density drilling fluid, which comprises the following raw materials in parts by weight; oil phase: 80-95 parts of a modifier; a main emulsifier: 2-4 parts; auxiliary emulsifier: 2-4 parts; wetting agent: 2-4 parts; organic soil: 0.5-3 parts; fluid loss additive: 2-6 parts; flow pattern regulator: 0-3 parts of a solvent; pressure-bearing plugging agent while drilling: 2-8 parts; composite plugging agent with variable particle size: 1-4 parts; lime: 2-4 parts; ultra-fine calcium carbonate: 3-5 parts; 25% CaCl2 saline: 5-20 parts of a solvent; API standard barite: the weight is increased to 2.05-2.3 g/cm 3. The drilling-while-drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system is high in thermal stability under a high-temperature condition, easy to regulate and control drilling fluid rheological property, high in plugging performance while drilling and simple in performance maintenance.)

1. The oil-based high-temperature high-density drilling fluid for the well drilling wall strengthening type rock gas reservoir is characterized by comprising the following raw materials in parts by weight;

oil phase: 80-95 parts of a modifier;

a main emulsifier: 2-4 parts;

auxiliary emulsifier: 2-4 parts;

wetting agent: 2-4 parts;

organic soil: 0.5-3 parts;

fluid loss additive: 2-6 parts;

flow pattern regulator: 0-3 parts of a solvent;

pressure-bearing plugging agent while drilling: 2-8 parts;

composite plugging agent with variable particle size: 1-4 parts;

lime: 2-4 parts;

ultra-fine calcium carbonate: 3-5 parts;

25% CaCl2 saline: 5-20 parts of a solvent;

API standard barite: weighting to 2.05-2.3 g/cm 3;

the pressure-bearing plugging agent while drilling is a well wall reinforcer which is formed by mixing acid-soluble rigid particles, elastic particles, micro fibers and softening particles through a double-helix conical mixer and improves the pressure-bearing capacity while drilling;

the proportion of the acid-soluble fresh-keeping particles, the elastic particles, the micro fibers and the asphalt softening particles is (0.5-3): (1-2): (3-5): (0.5 to 2);

the blocking agent with the variable particle size is prepared from styrene, butyl acrylate, nano silicon dioxide, divinylbenzene and sodium dodecyl sulfate through an emulsion polymerization method, and the median particle size of the blocking agent is distributed at 50-800 nm;

the main emulsifier and the auxiliary emulsifier are fatty acid ester surfactants;

the main component of the API standard barite is barium sulfate, and the density is more than or equal to 4.2g/cm 3;

the oil phase is No. 5 white oil, No. 3 white oil or diesel oil.

2. The drilling wall reinforced rock gas reservoir oil-based high-temperature high-density drilling fluid as claimed in claim 1, wherein the drilling fluid system is suitable for drilling engineering of a shale gas reservoir, the temperature resistance is over 180 ℃, and the density can reach 2.05-2.3 g/cm 3.

3. The oil-based high-temperature high-density drilling fluid for the wall-drilling reinforced rock-gas reservoir according to claim 1, wherein the drilling site construction process comprises the following steps;

s1, adding a main emulsifier, an auxiliary emulsifier and a wetting agent into an oil phase, wherein the oil phase can be No. 5 white oil, No. 3 white oil or diesel oil, and continuously stirring for 4-6 hours to form oil-based base slurry;

s2, and then gradually adding 25% CaCl2 saline water during stirring to form a mixture with an oil-water ratio of 8: 2, continuously stirring the water-in-oil drilling fluid simple system for 6 to 12 hours;

s3, respectively adding organic soil, a filtrate reducer, a flow pattern regulator, a pressure bearing plugging agent while drilling, a composite plugging agent with variable particle size, lime, superfine calcium carbonate and API standard barite under the stirring condition, and continuously stirring and maintaining to form a stable colloidal suspension system;

and S4, gradually establishing circulation of drilling fluid from a mud tank, entering a well, descending the well, exiting the well and the mud tank under the conveying of a mud pump, emptying or recovering old mud replaced in the shaft, and starting the high-temperature and high-pressure drilling operation of the shale gas reservoir.

Technical Field

The invention relates to the technical field of drilling fluid in petroleum and natural gas drilling engineering, in particular to a drilling wall reinforced type oil-based high-temperature high-density drilling fluid for a rock-gas reservoir.

Background

Shale gas resource reserves in China are abundant, geological resource reserves are preliminarily predicted to be about 134 multiplied by 1012m3, the technical recoverable reserve can be up to about 25 multiplied by 1012m3, and the shale gas resource reserves have wide development prospects and are important measures for solving the shortage of oil gas resources in China, realizing the increase of oil gas storage and production and guaranteeing the national energy safety.

The Chongqing district has abundant natural gas resources through early exploration, but has complex geological conditions, and shows that reservoir burial depth and transverse distribution are uneven, micro-nano hole seams of a shale reservoir develop, so that complex downhole problems such as well leakage, borehole wall instability and the like are easily caused in the drilling process, the drilling period is long, the drilling cost is high, severe tests and challenges are brought to the current shale reservoir drilling engineering, and the shale gas economic efficient exploration and development pace is severely restricted.

At present, a shale gas reservoir horizontal well drilling fluid technology is one of core technologies for shale gas resource development. In the initial stage of shale gas exploration and development in China, oil-based drilling fluid is generally selected for drilling of shale gas reservoir horizontal wells, because the oil-based drilling fluid has natural and good mud shale hydration inhibition performance, the oil-based drilling fluid can effectively inhibit hydration expansion and hydration dispersion of clay minerals in shale reservoirs, meanwhile, the oil-based drilling fluid has natural and good lubricity, the system composition of the oil-based drilling fluid is relatively simple, the rheological property is easy to adjust, and the requirements of good borehole purification and low annular circulation pressure drop can be met.

The shale gas reservoir is mostly composed of hard brittle shale, mainly consists of illite and an illite-montmorillonite mixed layer, and is an important reason for borehole wall instability caused by pore pressure transmission of the hard brittle shale. Therefore, the key to maintaining the stability of the well wall is to prevent pore pressure transmission, which must enhance the effective plugging of the micropores and microcracks. The shale has extremely low permeability and extremely small pore throat size, the traditional plugging agent is difficult to form effective mud cakes on the surface of the shale to prevent liquid phase invasion, and only micro-nano-scale particles can effectively plug the pore throat of the shale to prevent the liquid phase from invading the shale stratum, thereby being beneficial to maintaining the stability of a well wall.

The nanometer material has a huge specific surface area, so that the nanometer material can carry a large number of functional groups to meet special functional requirements, the nanometer particles have a tiny size (much smaller than the pore throat of a shale reservoir), and can easily enter the micropores of a shale matrix, generate physical plugging on the shale surface and effective chemical inhibition on the inner surface and the outer surface of clay, eliminate the interaction between shale and drilling fluid, reduce the damage or deformation of shale microstructure units, increase the capacity of resisting borehole wall collapse and cracking, widen a safety density window, and macroscopically enhance the stability of the shale borehole wall.

The inorganic nano particles are low in price and simple in preparation conditions, and are tried to be used for preparing the water-based drilling fluid nano treating agent at the earliest time. The modified nano-particles are introduced into the water-based drilling fluid by Qiuzongsong and other students in China at an early stage, and the rule of the influence of the nano-materials on the temperature resistance, the filtration loss and the shale permeability of the drilling fluid is discussed. Shale permeability is significantly reduced when certain nanoparticles are added to the drilling fluid. The organic nano particles can be compressed and deformed under certain temperature and pressure, can perform self-adaptive compact plugging on tiny gaps of well wall rocks, and are tried to be used for modifying drilling fluid by researchers. In addition, researchers have also attempted to prepare water-based nanofluidic fluids using both organic and inorganic nanoparticles.

However, in the existing drilling process, the bearing capacity of the shale reservoir is improved by a method while drilling, so that the problems of borehole wall collapse and fractured loss caused by high-density oil-based drilling fluid are solved.

Disclosure of Invention

The invention aims to provide a drilling wall reinforced type oil-based high-temperature high-density drilling fluid for a rock-gas reservoir, which aims to solve the problems that the pressure bearing capacity of the shale reservoir is improved by a drilling method in the existing drilling process, so that the well wall collapse and the high-density oil-based drilling fluid induce the fracture leakage are avoided.

In order to achieve the purpose, the invention provides the following technical scheme: the oil-based high-temperature high-density drilling fluid for the well drilling wall strengthening type rock gas reservoir comprises the following raw materials in parts by weight;

oil phase: 80-95 parts of a modifier;

a main emulsifier: 2-4 parts;

auxiliary emulsifier: 2-4 parts;

wetting agent: 2-4 parts;

organic soil: 0.5-3 parts;

fluid loss additive: 2-6 parts;

flow pattern regulator: 0-3 parts of a solvent;

pressure-bearing plugging agent while drilling: 2-8 parts;

composite plugging agent with variable particle size: 1-4 parts;

lime: 2-4 parts;

ultra-fine calcium carbonate: 3-5 parts;

25% CaCl2 saline: 5-20 parts of a solvent;

API standard barite: weighting to 2.05-2.3 g/cm 3;

the pressure-bearing plugging agent while drilling is a well wall reinforcer which is formed by mixing acid-soluble rigid particles, elastic particles, micro fibers and softening particles through a double-helix conical mixer and improves the pressure-bearing capacity while drilling;

the proportion of the acid-soluble fresh-keeping particles, the elastic particles, the micro fibers and the asphalt softening particles is (0.5-3): (1-2): (3-5): (0.5 to 2);

the blocking agent with the variable particle size is prepared from styrene, butyl acrylate, nano silicon dioxide, divinylbenzene and sodium dodecyl sulfate through an emulsion polymerization method, and the median particle size of the blocking agent is distributed at 50-800 nm;

the main emulsifier and the auxiliary emulsifier are fatty acid ester surfactants;

the main component of the API standard barite is barium sulfate, and the density is more than or equal to 4.2g/cm 3;

the oil phase is No. 5 white oil, No. 3 white oil or diesel oil.

Furthermore, the drilling fluid system is suitable for shale gas reservoir drilling engineering, the temperature resistance reaches over 180 ℃, and the density can reach 2.05-2.3 g/cm 3.

Further, the drilling site construction process comprises the following steps;

s1, adding a main emulsifier, an auxiliary emulsifier and a wetting agent into an oil phase, wherein the oil phase can be No. 5 white oil, No. 3 white oil or diesel oil, and continuously stirring for 4-6 hours to form oil-based base slurry;

s2, and then gradually adding 25% CaCl2 saline water during stirring to form a mixture with an oil-water ratio of 8: 2, continuously stirring the water-in-oil drilling fluid simple system for 6 to 12 hours;

s3, respectively adding organic soil, a filtrate reducer, a flow pattern regulator, a pressure bearing plugging agent while drilling, a composite plugging agent with variable particle size, lime, superfine calcium carbonate and API standard barite under the stirring condition, and continuously stirring and maintaining to form a stable colloidal suspension system;

and S4, gradually establishing circulation of drilling fluid from a mud tank, entering a well, descending the well, exiting the well and the mud tank under the conveying of a mud pump, emptying or recovering old mud replaced in the shaft, and starting the high-temperature and high-pressure drilling operation of the shale gas reservoir.

Compared with the prior art, the invention has the beneficial effects that:

the drilling-while-drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system is high in thermal stability under a high-temperature condition, easy to regulate and control drilling fluid rheological property, high in plugging performance while drilling and simple in performance maintenance.

Detailed Description

In the case of the example 1, the following examples are given,

in the embodiment of the invention, the oil-based high-temperature high-density drilling fluid for the well drilling wall strengthening type rock-gas reservoir comprises the following raw materials in parts by weight;

oil phase: 80-95 parts of a modifier;

a main emulsifier: 2-4 parts;

auxiliary emulsifier: 2-4 parts;

wetting agent: 2-4 parts;

organic soil: 0.5-3 parts;

fluid loss additive: 2-6 parts;

flow pattern regulator: 0-3 parts of a solvent;

pressure-bearing plugging agent while drilling: 2-8 parts;

composite plugging agent with variable particle size: 1-4 parts;

lime: 2-4 parts;

ultra-fine calcium carbonate: 3-5 parts;

25% CaCl2 saline: 5-20 parts of a solvent;

API standard barite: weighting to 2.05-2.3 g/cm 3;

the pressure-bearing plugging agent while drilling is a well wall reinforcer which is formed by mixing acid-soluble rigid particles, elastic particles, micro fibers and softening particles through a double-helix conical mixer and improves the pressure-bearing capacity while drilling;

the proportion of the acid-soluble fresh-keeping particles, the elastic particles, the micro fibers and the asphalt softening particles is (0.5-3): (1-2): (3-5): (0.5 to 2);

the blocking agent with the variable particle size is prepared from styrene, butyl acrylate, nano silicon dioxide, divinylbenzene and sodium dodecyl sulfate through an emulsion polymerization method, and the median particle size of the blocking agent is distributed at 50-800 nm;

the main emulsifier and the auxiliary emulsifier are fatty acid ester surfactants;

the main component of the API standard barite is barium sulfate, and the density is more than or equal to 4.2g/cm 3;

the wetting agent, the organic soil, the filtrate reducer, the flow pattern regulator, the lime and the 25 percent CaCl2 brine are all field conventional products.

The oil phase is No. 5 white oil, No. 3 white oil or diesel oil.

Wherein, the main emulsifier is HIEMUL, the auxiliary emulsifier is HICOAT, the wetting agent is HIWET, the organic soil is taken from the scene, and the product standard accords with the organic soil technical specification for QSY 1817-2015 oil-based drilling fluid.

The filtrate reducer is sulfonated resin BZ-PFL, the product standard conforms to the enterprise product standard of Q/12SYBHZ Bohai drilling engineering company, the flow pattern regulator is polyamide BZ-ORM, the product standard conforms to the enterprise product standard of Q/12SYBHZ Bohai drilling engineering company,

the pressure-bearing plugging agent while drilling is CLG-SZ.

The drilling fluid system is suitable for drilling engineering of shale gas reservoirs, the temperature resistance reaches over 180 ℃, and the density can reach 2.05-2.3 g/cm 3.

The variable-particle-size blocking agent CLG-NM is prepared from styrene, butyl acrylate, nano silicon dioxide, divinylbenzene and sodium dodecyl sulfate by an emulsion polymerization method, and the median particle size of the blocking agent is 50-800 NM.

The lime is calcium oxide; the mesh number of the superfine calcium carbonate is 400 meshes; CaCl₂Is an industrial product; the barite is API standard barite, and the density is not less than 4.2g/cm³。

In the case of the example 2, the following examples are given,

a well wall strengthening while drilling type shale gas reservoir oil-based high-temperature high-density drilling fluid system comprises the following raw materials in parts by weight:

oil phase: 80-85 parts of a solvent;

a main emulsifier: 3-3.5 parts;

auxiliary emulsifier: 3-3.5 parts;

wetting agent: 3-4 parts;

organic soil: 2-3 parts of a solvent;

fluid loss additive: 4-5 parts;

flow pattern regulator: 1-2 parts;

pressure-bearing plugging agent while drilling: 5-6 parts;

composite plugging agent with variable particle size: 3-4 parts;

lime: 2-3 parts of a solvent;

ultra-fine calcium carbonate: 3-4 parts;

25% CaCl2 saline: 18-20 parts of a solvent;

API standard barite: the weight is increased to 2.05-2.3 g/cm 3.

The density adjustable range of the drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system is 2.05-2.3 g/cm3, the medium-pressure filtration loss of an API (American Petroleum institute) is less than or equal to 0.5mL, the high-temperature high-pressure filtration loss at 180 ℃ and under the pressure difference of 3.5MPa is less than or equal to 3mL, and the rolling recovery rate of shale reservoir rock debris is more than or equal to 98%.

The while-drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system has the temperature resistance of up to 180 ℃, is suitable for being applied to shale reservoir drilling engineering of deep fractured formation development, and has the advantages of strong thermal stability under the high-temperature condition, easy regulation and control of drilling fluid rheological property, strong plugging performance while drilling and simple performance maintenance.

In the well wall strengthening while drilling type shale gas reservoir oil-based high-temperature high-density drilling fluid system, all the raw materials can be purchased commercially and all the qualified common industrial products can be obtained.

The invention relates to a preparation method of a well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system while drilling, which comprises the following steps:

under the condition of high-speed stirring (10000-12000 rpm), after the oil phase, the main emulsifier, the auxiliary emulsifier and the wetting agent are put into a high-speed stirring cup, the high-speed stirring is carried out for more than 30min, and then 25% of CaCl is added₂Stirring with saline water at high speed for 30min to form water-in-oil emulsion; then, respectively adding the mixture into a high-stirring cupAdding organic soil, a filtrate reducer, a flow pattern regulator, a pressure-bearing plugging agent while drilling, a composite plugging agent with variable particle size and lime, wherein after adding one treating agent, stirring at a high speed for 20min, adding the other treating agent; finally, weighting the oil-based drilling fluid to 2.05-2.3 g/cm by using API standard barite³And stirring at a high speed for 30min to obtain the drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system.

According to the characteristics of the field, the oil-based high-temperature high-density drilling fluid system for the well wall strengthening type shale gas reservoir while drilling is generally prepared on the drilling site.

Generally applied to the drilling engineering of a reservoir stratum with shale fractured development, the applicable temperature is less than or equal to 180 ℃, the drilling field application process method comprises the following steps,

wherein, the drilling site construction process comprises the following steps;

the field application process method comprises the following steps:

stopping drilling before drilling to a shale gas high-temperature fractured development stratum, emptying or recovering old slurry in a slurry tank, and injecting an oil blending phase into the slurry tank;

s1, adding a main emulsifier, an auxiliary emulsifier and a wetting agent into an oil phase, wherein the oil phase can be No. 5 white oil, No. 3 white oil or diesel oil, and continuously stirring for 4-6 hours to form oil-based base slurry;

s2, and then gradually adding 25% CaCl2 saline water during stirring to form a mixture with an oil-water ratio of 8: 2, continuously stirring the water-in-oil drilling fluid simple system for 6 to 12 hours;

s3, respectively adding organic soil, a filtrate reducer, a flow pattern regulator, a pressure bearing plugging agent while drilling, a composite plugging agent with variable particle size, lime, superfine calcium carbonate and API standard barite under the stirring condition, and continuously stirring and maintaining to form a stable colloidal suspension system;

and S4, gradually establishing circulation of drilling fluid from a mud tank, entering a well, descending the well, exiting the well and the mud tank under the conveying of a mud pump, emptying or recovering old mud replaced in the shaft, and starting the high-temperature and high-pressure drilling operation of the shale gas reservoir.

Wherein, the test method adopted by the invention is according to GB/T16783.2-2012' petroleum and natural gas industry drilling fluid field test part 2: oil-based drilling fluids. The raw materials, reagents and the like used in the examples are commercially available unless otherwise specified. The oil phase is No. 5 white oil, a main emulsifier HIEMUL, an auxiliary emulsifier HICOAT, a wetting agent HIWET, organic soil, a fluid loss additive sulfonated resin BZ-PFL, a flow pattern regulator polyamide BZ-ORM, superfine calcium carbonate and API standard barite are all taken from Wei page 27-9HF drilling sites of Weirong shale gas exploration and development blocks of the Miyam petrochemical southwestern oil and gas field division company; the pressure-bearing plugging agent CLG-SZ while drilling is purchased from Chengdu Desheng geological exploration technology, Inc.; the composite plugging agent CLG-NM with variable particle size is prepared by laboratories; lime and CaCl2 were purchased from the national pharmaceutical group chemicals.

1.1 formula composition of the high-temperature high-density oil-based drilling fluid:

320mL of No. 5 white oil, 12g of main emulsifier HIEMUL, 12g of auxiliary emulsifier HICOAT, 12g of wetting agent HIWET, 80mL of 25% CaCl2 saline water, 12g of organic soil, 16g of fluid loss additive BZ-PFL, 8g of flow type regulator BZ-ORM, 20g of pressure-bearing plugging agent while drilling CLG-SZ, 12g of particle size-variable composite plugging agent CLG-NM, 8g of lime, 12g of superfine calcium carbonate and barite are weighted to 2.2g/cm 3.

1.2 the preparation method comprises the following steps: adding 320mL of No. 5 white oil, 12g of main emulsifier HIEMUL, 12g of auxiliary emulsifier HICOAT and 12g of wetting agent HIWET into a high-stirring cup, stirring at a high speed (8000-12000 rpm) for 30min, adding 80mL of 25% CaCl2 saline, and stirring at a high speed for 30min to form a stable emulsion system; then, respectively adding 12g of organic soil, 16g of filtrate reducer BZ-PFL, 8g of flow pattern regulator BZ-ORM, 20g of pressure bearing while drilling plugging agent CLG-SZ, 12g of particle size variable composite plugging agent CLG-NM, 8g of lime and 12g of superfine calcium carbonate in a high-stirring cup in sequence, wherein after adding each treating agent, stirring at a high speed for 20min, adding the other treating agent; and finally, weighting the oil-based drilling fluid to 2.2g/cm3 by using API standard barite, and stirring at a high speed for 30min to obtain the drilling-while-drilling well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system. As a test slurry for the following drilling fluid performance tests.

1.3 drilling fluid basic performance test:

and (3) putting the prepared drilling fluid into an aging tank, respectively carrying out hot rolling for 16 hours at 150 ℃ and 180 ℃, cooling to room temperature, and transferring into a high-speed stirring cup to stir for 20 minutes at a high speed. The viscosity, shear force, medium pressure fluid loss and high temperature and high pressure fluid loss (180 ℃/3.5MPa) of each test slurry were measured, wherein the test temperature for rheology was 65 ℃, and the test results are shown in table 1.

Drilling fluid Performance test results in Table 1 example

As can be seen from Table 1, after the test slurry is aged at high temperature, the apparent viscosity and the plastic viscosity are slightly increased, the dynamic shear force is maintained at 11-20.5Pa, the initial cut and the final cut are basically kept stable, the API (American Petroleum institute) filtration loss is 0mL, the HTHP filtration loss is less than 3mL, the breaking voltage shows a trend of gradually increasing along with the continuous increase of the high-temperature aging temperature, and the stability of the emulsion of the well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system while drilling under the high-temperature condition is better.

1.4 inhibition performance test:

and respectively testing the shale rolling recovery rate test under the condition of 77 ℃ after the clean water, the test slurry and the test slurry are respectively subjected to high-temperature hot rolling for 16 hours at 150 ℃ and 180 ℃. The results of the experiment are shown in table 2.

TABLE 2 shale Rolling recovery test results

As can be seen from Table 2, the recovery rate of the selected shale reservoir rock sample in clear water is only 32.6%, which shows that the shale has stronger hydration dispersion characteristics, and the recovery rates of the shale in test slurry and the test slurry aged at 150 ℃ and 180 ℃ respectively are higher than 98%, which shows that the well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system while drilling has excellent characteristics of inhibiting the hydration dispersion of the shale.

1.5 test of pressure-bearing plugging performance while drilling:

by means of a low-permeability sand disc (PPA sand disc) plugging performance evaluation instrument (OFITE type), the plugging performance of the on-site drilling fluid on a low-permeability sand disc with the permeability of 3 mu m2 is evaluated after the on-site drilling fluid is aged at 150 ℃/16h under the evaluation conditions of filter element number Fann Fliter Discs 210536 (permeability 3 mu m2, gas measurement) and 1000psi and 150 ℃. The results of the experiment are shown in table 3.

TABLE 3 Experimental results of pressure-bearing plugging performance test while drilling

From the experimental results, the instantaneous filtration loss, the static filtration rate and the PPA leakage loss measured in the PPA experiment of the field well slurry of the Welan 28-7HF well and the field well slurry of the Welan 27-9HF well of the two wells sampled on site are larger than the numerical values of the test slurry, and the results show that the well wall strengthening type shale gas reservoir oil-based high-temperature high-density drilling fluid system while drilling has remarkable plugging and pressure-bearing capacity.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.