阅读说明：本技术 端部脱砂压裂方法 (End sand-removing fracturing method ) 是由 张仲春 张瑞 李建芳 于 2019-10-23 设计创作，主要内容包括：本发明涉及油田压裂酸化技术领域,是一种端部脱砂压裂方法；第一步,向压裂地层泵入前置液；第二步,待压裂地层的主裂缝长达到压裂设计目标值时,泵入高效降滤失液；第三步,泵入高效降滤失液待压力增加时泵入携砂液；第四步,注入顶替液,测试油气产量。本发明在泵入高效降滤失液时不用改变施工排量,施工程序简单,便于现场操作,本发明中的高效降滤失液中含有助排剂、粘土稳定剂和破胶剂,可以降低滤液对储层的伤害,5小时后降滤失剂的剩余率在30%左右；同时本发明端部脱砂压裂方法较现有技术压裂后产量提高了80%至160%,稳产期较现有技术压裂后提高了2倍至3倍,采用本发明压裂后增产效果明显,没有发生临井压窜现象。(The invention relates to the technical field of fracturing and acidizing of oil fields, in particular to a method for end desanding and fracturing; firstly, pumping a pad fluid into a fractured stratum; secondly, pumping high-efficiency fluid loss additive when the length of the main crack of the stratum to be fractured reaches a fracturing design target value; thirdly, pumping the high-efficiency filtrate reducing fluid and pumping the sand carrying fluid when the pressure is increased; and fourthly, injecting displacement liquid and testing the oil gas yield. The construction discharge amount is not required to be changed when the high-efficiency fluid loss additive is pumped, the construction process is simple, the field operation is convenient, the high-efficiency fluid loss additive contains a cleanup additive, a clay stabilizer and a gel breaker, the damage of filtrate to a reservoir can be reduced, and the residual rate of the fluid loss additive is about 30% after 5 hours; meanwhile, compared with the prior art, the end desanding fracturing method improves the yield by 80 to 160 percent, improves the stable yield period by 2 to 3 times, has obvious yield-increasing effect after fracturing, and does not have the phenomenon of well-approaching pressure channeling.)

1. An end sand-removing fracturing method is characterized by comprising the following steps: firstly, pumping a pad fluid into a fractured stratum; secondly, pumping high-efficiency fluid loss additive when the length of the main crack of the stratum to be fractured reaches a fracturing design target value; thirdly, pumping the high-efficiency filtrate reducing fluid and pumping the sand carrying fluid when the pressure is increased; fourthly, injecting displacement fluid, closing the well for 2 to 6 hours, opening the well, discharging the fluid, and testing the oil gas yield; wherein: the volume ratio of the pumped pad fluid to the high-efficiency fluid loss additive to the pumped sand carrying fluid is 10-100: 4 to 70: 30 to 300.

2. The end screenout fracturing method of claim 1, wherein the high efficiency fluid loss fluid comprises, by mass, 0.2% to 0.5% of a guanidine gum base fluid, 1% to 20% of a fluid loss additive, 1% to 10% of a gel breaker, 0.2% to 2% of a cleanup additive, 0.4% to 1% of a clay stabilizer, and the balance of water; or/and adjusting the pH value of the high-efficiency fluid loss additive to 8.5-11 by using sodium hydroxide or sodium carbonate before pumping the high-efficiency fluid loss additive.

3. The end screenout fracturing method of claim 2, wherein the fluid loss additive comprises 85 to 90 parts by weight of bulk-expanded polymer particles, 10 to 15 parts by weight of coating material and 0.5 to 1 part by weight of particle dispersant.

4. The end screenout fracturing method of claim 3, wherein the fluid loss additive is obtained by: firstly, putting a proper amount of volume expanded polymer particles into coating equipment, rotating the coating equipment, introducing hot air into the coating equipment to preheat the volume expanded polymer particles to 30-40 ℃; secondly, preparing a required amount of coating material into a coating material solution; thirdly, spraying a coating material solution to the gaps of the preheated volume expansion polymer particles at the temperature of 30-40 ℃; fourthly, after the solvent in the coating material solution sprayed on the surface of the volume expansion polymer particles is taken away by hot air, the coating material is solidified on the surface of the volume expansion polymer particles in time; and fifthly, stopping rotating the coating equipment, adding the required amount of the particle dispersing agent into the coating equipment, uniformly mixing, and then cooling by ventilation to obtain the fluid loss additive.

5. The end screenout fracturing method of claim 4, wherein in the third step of fluid loss additive preparation, the preheated bulk-expanding polymer particles are sprayed with a coating material solution by a spray gun gap at a spray rate of 20ml to 50ml per 3 seconds; or/and, in the fourth step of fluid loss additive preparation, the thickness of the coating material solidified on the surface of the volume expanded polymer particles is 0.1mm to 1 mm; or/and in the fifth step of preparing the fluid loss additive, adding a required amount of particle dispersing agent into coating equipment, rotating for 10 to 30 minutes, introducing natural wind for cooling, and cooling to obtain the fluid loss additive.

6. The end-screenout fracturing method of claim 5, wherein the temperature of the hot air introduced into the coating equipment is 50 ℃ to 65 ℃, and the flow rate of the hot air is 10ml/min to 30 ml/min; or/and the rotating speed of the coating equipment is 100 to 150 revolutions per minute; or/and the coating material comprises A and a wetting agent, the coating material solution is ethanol or toluene solution of the coating material, the mass percent of A in the coating material solution is 50-80%, and the mass percent of the wetting agent in the coating material solution is 1-5%; wherein: a is more than one of methylcellulose, ethyl cellulose, hydroxypropyl methylcellulose, polyvinylpyrrolidone and liquid paraffin, and wetting agent is more than one of span 80 and span 20.

7. The end screenout fracturing method of claim 6, wherein the particulate dispersant is one or more of starch, magnesium carbonate, barium sulfate, calcium phosphate, talc and kaolin; or/and the particle size of the filtrate reducer is 14-25 meshes; or the particle size of the filtrate reducer is 35-45 meshes; or the particle size of the filtrate reducer is 60 meshes to 80 meshes.

8. The end screenout fracturing method of claim 1, 2, 3, 4, 5, 6 or 7, wherein the fracturing fluid used in the end screenout fracturing method is hydroxypropyl guar fracturing fluid, and the hydroxypropyl guar fracturing fluid contains 0.3 to 0.6 percent of hydroxypropyl guar powder, 0.5 to 2 percent of potassium chloride, 1 to 3 percent of cleanup additive, 0.01 to 0.8 percent of sodium carbonate or sodium hydroxide, 0.5 to 5 percent of cross-linking agent, 0.5 to 0.01 percent of persulfate and the balance of water according to mass percentage.

9. The end screenout fracturing method of claim 8, wherein the gel breaker is persulfate or hydrogen peroxide; a cleanup additive of the fluorocarbon type; the cross-linking agent is an organic boron cross-linking agent; the clay stabilizer is quaternary ammonium salt clay stabilizer.

10. The end screenout fracturing method of claim 9, wherein the persulfate is preferably ammonium persulfate or potassium persulfate; the excretion assistant is preferably KML-ZP excretion assistant; the crosslinking agent is preferably KML-YP organic boron crosslinking agent; the clay stabilizer is preferably KML-NT organic clay stabilizer.

Technical Field

The invention relates to the technical field of fracturing and acidizing of oil fields, in particular to a method for end sand removal fracturing.

Background

Hydraulic fracturing of medium and high permeability reservoirs, conventional low permeability reservoirs and tight well blocks to achieve high conductivity, end screenout fracturing (TSO) is the best choice. The application of TSO fracturing technology proposed by Smith et al (1984) revolutionized the well completion and production increase transformation technology of low and high permeability reservoirs.

97.6kg/m can be obtained by TSO fracturing technology²The proppant placement concentration of (a), which indicates that the conductivity can be increased by a factor of 10 to 20. Under high stress conditions, the conductivity can be improved by the same amount by using artificial proppant (corresponding to quartz sand), and the conductivity can be improved by nearly 100 times by combining the artificial proppant and the quartz sand. If the diversion is limited, the oil well capacity may be increased by 4 to 7 times.

The sand-removing fracturing Technology (TSO) is a hydraulic fracturing technology which forms a sand plug at the front end of a certain crack length to prevent the crack from extending, and simultaneously, continues to pump fracturing fluids with different proppant concentrations at a certain discharge capacity to force the crack to expand, so that a wider crack and a higher sand concentration are obtained, and the flow conductivity of the crack is improved. In the fracturing construction, fracturing fluid is pumped and injected into the bottom of a well by ground pumping equipment at a large discharge rate, the pumping speed of the fracturing fluid is far higher than the filtration rate of the stratum of a perforated layer section at the bottom of the well, the bottom pressure of the well is quickly raised, when the bottom pressure reaches the stratum fracture pressure, stratum rocks start to generate cracks, and fracturing pad fluid immediately enters the cracks. And under the condition that the injection speed is higher than the liquid filtration speed, the crack continues to expand, and after the front pad fluid completely enters the crack, the front pad fluid is less and less due to continuous filtration towards the stratum, and finally the whole fluid is completely filtered into the stratum. At this time, the crack front reaches the end of the crack front with a small crack width, and sand therein is stuck between the crack wall surfaces having a certain hardness and does not flow any more. And when the liquid supply speed and the fluid loss speed reach dynamic balance, the pressure of the zone gradually drops to be lower than the pressure required for crack expansion, so that the crack cannot be expanded continuously in the crack length and height directions. Under the condition of constant liquid pumping speed at the ground, the expansion speed of the crack volume is gradually increased due to the fact that the fluid loss speed is smaller and smaller, namely the increasing speed of the crack width is increased. The above-described screenout fracturing process continues until the fracture width or bottom hole pressure reaches a design limit. Therefore, the sand-removing fracturing of the end part of the crack can control the length and the height of the crack to a certain extent, obtain larger crack width and form a short-wide crack.

The existing end desanding technology has certain technical limitation, in the end fracturing process, the viscosity of the fracturing fluid is lower than that of the conventional fracturing fluid, the requirement on the viscosity of the fracturing fluid is stricter than that of the conventional fracturing, and the viscosity requirement of the fracturing fluid subjected to end desanding fracturing meets two mutually contradictory aspects: firstly, the liquid is ensured to suspend sand, and secondly, the sand removal around the crack is facilitated. If the viscosity is too low, the sand suspension cannot be ensured in the seam, a sand-free area can appear on the upper part of the seam, and the purpose of peripheral sand removal cannot be achieved: the viscosity is too high, the peripheral filtration loss is too slow, and the timely sand removal of the periphery is difficult to realize. In addition, under the condition that a certain crack length is formed by the pad fluid, in order to achieve the end desanding effect, a section of sand carrying fluid with low sand concentration needs to be added, the fracturing fluid efficiency is 50% during desanding, and in order to increase the hydraulic fracture width by two times, the total fluid quantity needing to be injected is 1.8 times of the fluid quantity injected before desanding, so that the fracturing cost and the risk of damage of the filtrate to the permeability of a reservoir stratum are increased. Therefore, in practical application, the performance of the end desanding liquid is difficult to grasp, and the probability of successfully realizing end desanding fracturing construction is low. With the continuous and deep development of various oil and gas fields, the yield increasing effect is not obvious after a plurality of oil and gas wells are fractured; the phenomenon is mostly manifested as poor gas production, rapid decrease of pressure and yield after pressing, short stable production period or adjacent well pressure channeling.

Disclosure of Invention

The invention provides an end desanding fracturing method, which overcomes the defects of the prior art and can effectively solve the problem that the yield increasing effect is always not obvious after the fracturing of the conventional oil and gas well; the problems of poor gas production, rapid decrease of pressure and yield after the pressure, short stable production period or adjacent well pressure channeling are mostly presented.

The technical scheme of the invention is realized by the following measures: an end sand-removing fracturing method comprises the following steps: firstly, pumping a pad fluid into a fractured stratum; secondly, pumping high-efficiency fluid loss additive when the length of the main crack of the stratum to be fractured reaches a fracturing design target value; thirdly, pumping the high-efficiency filtrate reducing fluid and pumping the sand carrying fluid when the pressure is increased; fourthly, injecting displacement fluid, closing the well for 2 to 6 hours, opening the well, discharging the fluid, and testing the oil gas yield; wherein: the volume ratio of the pumped pad fluid to the high-efficiency fluid loss additive to the pumped sand carrying fluid is 10-100: 4 to 70: 30 to 300.

The following is further optimization or/and improvement of the technical scheme of the invention:

the high-efficiency fluid loss additive comprises, by mass, 0.2% to 0.5% of a guanidine gum base fluid, 1% to 20% of a fluid loss additive, 1% to 10% of a gel breaker, 0.2% to 2% of a cleanup additive, 0.4% to 1% of a clay stabilizer, and the balance of water; or/and adjusting the pH value of the high-efficiency fluid loss additive to 8.5-11 by using sodium hydroxide or sodium carbonate before pumping the high-efficiency fluid loss additive.

The raw materials of the fluid loss agent comprise 85 to 90 parts of volume expansion polymer particles, 10 to 15 parts of coating materials and 0.5 to 1 part of particle dispersing agents according to parts by weight.

The filtrate reducer is obtained by the following method: firstly, putting a proper amount of volume expanded polymer particles into coating equipment, rotating the coating equipment, introducing hot air into the coating equipment to preheat the volume expanded polymer particles to 30-40 ℃; secondly, preparing a required amount of coating material into a coating material solution; thirdly, spraying a coating material solution to the gaps of the preheated volume expansion polymer particles at the temperature of 30-40 ℃; fourthly, after the solvent in the coating material solution sprayed on the surface of the volume expansion polymer particles is taken away by hot air, the coating material is solidified on the surface of the volume expansion polymer particles in time; and fifthly, stopping rotating the coating equipment, adding the required amount of the particle dispersing agent into the coating equipment, uniformly mixing, and then cooling by ventilation to obtain the fluid loss additive.

In the third step of preparing the fluid loss additive, spraying the coating material solution to the preheated volume-expanded polymer particles by using a spray gun gap, wherein the spraying speed of the spray gun gap is once every 3 seconds, and the spraying amount is 20ml to 50ml once; or/and, in the fourth step of fluid loss additive preparation, the thickness of the coating material solidified on the surface of the volume expanded polymer particles is 0.1mm to 1 mm; or/and in the fifth step of preparing the fluid loss additive, adding a required amount of particle dispersing agent into coating equipment, rotating for 10 to 30 minutes, introducing natural wind for cooling, and cooling to obtain the fluid loss additive.

The temperature of the hot air introduced into the coating equipment is 50-65 ℃, and the flow rate of the hot air is 10-30 ml/min; or/and the rotating speed of the coating equipment is 100 to 150 revolutions per minute; or/and the coating material comprises A and a wetting agent, the coating material solution is ethanol or toluene solution of the coating material, the mass percent of A in the coating material solution is 50-80%, and the mass percent of the wetting agent in the coating material solution is 1-5%; wherein: a is more than one of methylcellulose, ethyl cellulose, hydroxypropyl methylcellulose, polyvinylpyrrolidone and liquid paraffin, and wetting agent is more than one of span 80 and span 20.

The particle dispersing agent is more than one of starch, magnesium carbonate, barium sulfate, calcium phosphate, talcum powder and kaolin; or/and the particle size of the filtrate reducer is 14-25 meshes; or the particle size of the filtrate reducer is 35-45 meshes; or the particle size of the filtrate reducer is 60 meshes to 80 meshes.

The fracturing fluid used in the end desanding fracturing method is hydroxypropyl guar gum fracturing fluid which comprises 0.3 to 0.6 percent of hydroxypropyl guar gum powder, 0.5 to 2 percent of potassium chloride, 1 to 3 percent of cleanup additive, 0.01 to 0.8 percent of sodium carbonate or sodium hydroxide, 0.5 to 5 percent of cross-linking agent, 0.5 to 0.01 percent of persulfate and the balance of water according to mass percentage.

The gel breaker is persulfate or hydrogen peroxide; a cleanup additive of the fluorocarbon type; the cross-linking agent is an organic boron cross-linking agent; the clay stabilizer is quaternary ammonium salt clay stabilizer.

The persulfate is preferably ammonium persulfate or potassium persulfate; the excretion assistant is preferably KML-ZP excretion assistant; the crosslinking agent is preferably KML-YP organic boron crosslinking agent; the clay stabilizer is preferably KML-NT organic clay stabilizer.

The construction discharge amount is not required to be changed when the high-efficiency fluid loss additive is pumped, the construction process is simple, the field operation is convenient, the high-efficiency fluid loss additive contains a cleanup additive, a clay stabilizer and a gel breaker, the damage of filtrate to a reservoir can be reduced, and the residual rate of the fluid loss additive is about 30% after 5 hours; meanwhile, compared with the prior art, the end desanding fracturing method improves the yield by 80 to 160 percent and the stable yield period by 2 to 3 times, has obvious yield increasing effect after fracturing, does not generate the phenomenon of well-approaching pressure channeling, realizes the purposes of stable yield and increasing yield, and is suitable for the end desanding fracturing modification construction of oil and gas reservoirs with middle-high seepage old blocks, reservoir temperature less than or equal to 120 ℃ and reservoir depth less than or equal to 3000 m.

Drawings

FIG. 1 is a graph of polymer residue rate versus time in the present invention.

FIG. 2 is a graph showing the variation of oil pressure, displacement and sand ratio during the fracturing process.

FIG. 3 shows the oil layer data in Table 1.

FIG. 4 shows the scale of fracturing operations in Table 2.

FIG. 5 shows the performance indexes of the high-efficiency fluid loss control agent in Table 3.

FIG. 6 shows the performance index of the sand-carrying fluid of Table 4.

FIG. 7 shows the pump-injection procedure for the construction of Table 5.

Detailed Description

The present invention is not limited by the following examples, and specific embodiments may be determined according to the technical solutions and practical situations of the present invention. The various chemical reagents and chemical articles mentioned in the invention are all the chemical reagents and chemical articles which are well known and commonly used in the prior art, unless otherwise specified; the percentages in the invention are mass percentages unless otherwise specified; the solution in the present invention is an aqueous solution of water as a solvent, for example, a hydrochloric acid solution is an aqueous hydrochloric acid solution, unless otherwise specified.