Drilling fluid for extending shale collapse cycle and construction method thereof

Abstract

The present invention relates to a drilling fluid capable of extending the collapse period of shale in the field of oil and gas drilling and a construction method thereof. The drilling fluid capable of extending the collapse period of shale comprises the following components by weight: 3-4% sodium bentonite; 0.2-0.3% drilling fluid inhibitor; 5-7% potassium chloride; 0.8-1.5% salt-resistant and high-temperature resistant fluid loss reducer; 1-1.5% low-fluorescence anti-collapse agent; 1-1.5% anti-collapse fluid loss reducer; 1-3% environmentally friendly lubricant; 1-1.5% oil layer protectant; 1-1.5% micro-nano plugging agent; 1-1.5% biphilic pressure-bearing plugging agent; 1-6% weighting agent; 2-4% alkalinity regulator; and the remainder being water, totaling 100%. The drilling fluid system of the present invention has good rheological properties, low fluorescence level, strong wall-building ability under high temperature and high pressure, high plugging and pressure-bearing capacity, and can extend the collapse period of shale, thereby meeting the requirements for deep shale oil and gas discovery and safe drilling.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas drilling, and in particular to a drilling fluid system capable of extending the collapse period of shale and a construction method thereof. Background Art

[0002] To vigorously promote exploration and development, Jiangsu Oilfield has invested heavily in recent years in concealed reservoirs in the northern Jiangsu Basin. This has resulted in longer and longer shale intervals and more faults. This has increased the risk of shale wellbore instability and fracture-induced leakage during drilling, leading to longer drilling cycles. On-site efforts to reduce shale collapse by increasing drilling fluid density have achieved some success. However, some wells, due to excessively high drilling fluid density, have experienced varying degrees of lost circulation, significantly impacting oil and gas discoveries.

[0003] In recent years, both domestic and international efforts have been made to reduce downhole complexity and prolong the formation collapse cycle during exploration and development. A new oil and gas layer protective agent developed based on film-forming theory effectively prevents or delays drilling fluid filtrate from entering the formation through the molecular membrane effect, thus prolonging the wellbore collapse cycle. This oil layer protective agent contains sulfonated phenolic resin. The "Hazardous Waste Exclusion Management List (2021 Edition)" released in 2021 clearly defines "polysulfone system mud" as a hazardous waste. Sulfonated phenolic resin is an important treatment agent in the system, and its promotion and application are subject to certain restrictions. Secondly, a new high-temperature resistant plugging and anti-collapse agent based on oil-soluble resin has the advantages of being able to withstand temperatures of up to 180°C and can be tightly adsorbed on the rock surface, effectively reducing the intrusion of drilling fluid into shale microcracks and prolonging the wellbore collapse cycle. However, the disadvantage is that this treatment agent has a high fluorescence level, a low reduction rate in high-temperature and high-pressure filtration loss, and limited plugging capacity. At the same time, an effective drilling fluid plugging and anti-collapse system has not yet been formed. The ammonium-based polymer drilling fluid system mentioned in improving wellbore stability of horizontal wells in tight low-permeability oil and gas reservoirs is also developed only for tight low-permeability sandstone oil and gas layers, and is not a large reference type.

[0004] Therefore, in order to deal with the risks of wellbore instability, fracture leakage, and formation collapse in shale sections during oil and gas drilling, it is necessary to research and develop a drilling fluid system that has good rheological properties, strong wall-building properties, high sealing and pressure-bearing capacity, and low fluorescence level at high temperatures, which can comprehensively improve the pressure-bearing capacity of shale formations and extend the formation collapse cycle at the same actual drilling density, so as to fundamentally solve the needs of deep shale oil and gas discovery and safe drilling. Summary of the Invention

[0005] The present invention addresses the problem in the existing technology that it is difficult to balance wellbore stability, fracture leakage and oil and gas discovery under high density in drilling deep shale formations. The invention provides a drilling fluid system with good rheology, low fluorescence level, strong wall-building ability under high temperature and high pressure, high sealing and pressure-bearing capacity, and the ability to extend the shale collapse cycle, so as to meet the requirements of deep shale oil and gas discovery and safe drilling.

[0006] The present invention first provides a drilling fluid for extending the collapse period of mud shale. The drilling fluid for extending the collapse period of mud shale is characterized by comprising the following components by weight: 3-4% sodium bentonite; 0.2-0.3% drilling fluid inhibitor; 5-7% potassium chloride; 0.8-1.5% salt-resistant and high-temperature resistant fluid loss reducer; 1-1.5% low-fluorescence anti-collapse agent; 1-1.5% anti-collapse fluid loss reducer; 1-3% environmentally friendly lubricant; 1-1.5% oil layer protective agent; 1-1.5% micro-nano plugging agent; 1-1.5% biphilic pressure-bearing plugging agent; 1-6% weighting agent; 2-4% alkalinity regulator; and the remainder being water, totaling 100%.

[0007] The drilling fluid of the present application uses potassium chloride drilling fluid as the basic system, which is an inorganic salt shale inhibitor with a strong ability to inhibit shale penetration and hydration. It is combined with a low-fluorescence anti-collapse agent, an environmentally friendly nano-plugging agent and a biphilic pressure-bearing plugging agent as core treatment agents. Under high-temperature conditions, it has good rheology, strong wall-building ability (high-temperature and high-pressure filtration loss <6 ml), high plugging pressure-bearing capacity, and low fluorescence level. It is a drilling fluid system that comprehensively improves the pressure-bearing capacity of shale formations and extends the formation collapse cycle at the same actual drilling density. It has very important practical significance for fundamentally solving the problems of deep shale oil and gas discovery and safe drilling.

[0008] Furthermore, the low-fluorescence anti-slump agent is an environmentally friendly non-fluorescent anti-slump agent NFA-25. It is obtained by using high-carbon alcohol and high-carbon acid as the main raw materials through water-soluble modification, and has the effect of reducing the high-temperature and high-pressure filtration loss of drilling fluid.

[0009] Furthermore, the micro-nano plugging agent is an environmentally friendly nano plugging agent JS-G1, which is prepared by mixing modified elastic resin, modified rosin and a rigid plugging agent with a particle size of 100nm-10μm, and can effectively plug shale micro-cracks and prevent filtrate from invading the formation.

[0010] Furthermore, the drilling fluid inhibitor is a zwitterionic polymer FA367 with a molecular weight of 5 to 8 million. It is a water-soluble high molecular polymer copolymerized from a variety of anionic, nonionic, and organic ionic monomers. It has good water solubility and is salt-resistant and high-temperature-resistant and can inhibit shale dispersion.

[0011] Furthermore, the amphiphilic pressure-bearing plugging agent is an amphiphilic microsphere polymer material AMP composed of an oleophilic core and a hydrophilic shell. It has excellent temperature resistance and is compatible with the microcracks and micropore leakage channels in shale formations, significantly improving the pressure-bearing strength of the plugging layer. It also forms a hydrophobic film at the rock interface, further reducing filtrate intrusion into the formation.

[0012] Furthermore, the salt-resistant and high-temperature-resistant fluid loss reducer is polyanionic cellulose LV-PAC, which is a water-soluble cellulose ether derivative obtained by chemically modifying natural cellulose and has good high-temperature-resistant fluid loss reduction performance in drilling fluid.

[0013] Furthermore, the anti-collapse and fluid loss agent is the anti-collapse and fluid loss agent MFJ-1; it is a graft copolymer of potassium humate and cationic olefin monomers, and the synergistic effect of K+ and cations improves the anti-collapse effect, thereby reducing the risk of shale wellbore collapse; the oil layer protective agent is the ultra-low permeability treatment agent LXJ-1, which utilizes a special polymer treatment agent to concentrate on the wellbore rock surface to form micelles, forming a dense ultra-low permeability sealing membrane on the wellbore rock surface to prevent the filtrate from invading the shale formation.

[0014] Furthermore, the environmentally friendly lubricant is the water-based lubricant KD-21C or the environmentally friendly bio-lubricant JS-LUB; and the drilling fluid flow pattern regulator is the viscosity reducer MSO.

[0015] Furthermore, the alkalinity regulator is NaOH; the weighting agent is limestone powder CaCO3 or BaSO4.

[0016] The present invention also provides a method for applying drilling fluid for extending the collapse period of shale, comprising the following steps:

[0017] Construction preparation stage: Drilling is carried out in the upper part of the shale section using zwitterionic polymer drilling fluid. 200-300 m into the shale section, the drilling fluid properties are adjusted to ensure that the density meets the formation pressure and wellbore safety requirements. The bentonite content is controlled at 20-30 g / l, and the viscosity is reduced to PV of 8-15 mPa.s and YP of 3-5 Pa.

[0018] System conversion stage: Add 0.2% to 0.3% drilling fluid inhibitor and 0.8% to 1.5% salt and high temperature resistant fluid loss reducer to the drilling fluid adjusted in the construction preparation stage in order by mass proportion. After circulating the mud pump for 1 to 2 weeks, add 5% to 7% potassium chloride in time and circulate it for another 1 to 2 weeks to convert it into a potassium chloride drilling fluid basic system.

[0019] Mixing adjustment: When drilling into mud shale, promptly add 1% to 1.5% of low-fluorescence anti-collapse agent and 1% to 1.5% of anti-collapse and fluid loss agent to the basic system during the system conversion stage; when drilling into mud shale with developed microcracks, promptly add 1% to 1.5% of micro-nano plugging agent and 1% to 1.5% of bifacial pressure-bearing plugging agent;

[0020] Performance maintenance: When drilling in shale wells, add 4% to 6% of low-fluorescence anti-collapse agent and 4% to 6% of anti-collapse and fluid loss agent in a timely manner for every 100±1m of drilling progress. When drilling in shale with developed microfractures, add 4% to 6% of low-fluorescence anti-collapse agent and 4% to 6% of anti-collapse and fluid loss agent in a timely manner for every 100±1m of drilling progress. Also, add 4% to 6% of micro-nano plugging agent and, in a timely manner, bi-philic pressure-bearing plugging agent in a timely manner.

[0021] Reservoir protection: Drill into the first 50m of the reservoir and add 1% to 1.5% of the oil layer protection agent at one time;

[0022] Completion preparation: Before electrical logging and casing running, add 1% to 3% environmentally friendly lubricant to the drilling fluid according to the needs of wellbore lubrication and anti-sticking.

[0023] The present invention provides a construction method for the drilling fluid for extending the shale collapse period. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the changing curve of the influence of potassium ammonium based polymer drilling fluid on the collapse cycle of shale.

[0025] Figure 2 The graph is a regular curve showing the influence of the drilling fluid of the present invention on the collapse cycle of shale. Implementation Method

[0026] The following describes in detail the maintenance process of drilling in deep shale formations using the drilling fluid for extending the shale collapse period of the present invention with reference to the accompanying drawings. Example

[0027] When drilling the deep shale section of the Y1-2 lateral well in Jiangsu Oilfield, according to the construction requirements of the formation stress of the target block, the raw material components and mass proportions are as follows: 40 parts of sodium bentonite; 2 parts of the zwitterionic polymer of the drilling fluid inhibitor FA367; 70 parts of potassium chloride powder; 8 parts of the salt-resistant and high-temperature resistant fluid loss reducer LV-PAC; 15 parts of the low-fluorescence anti-collapse agent NFA-25; 15 parts of the anti-collapse fluid loss reducer MFJ-1; 20 parts of the environmentally friendly lubricant KD-21C; 15 parts of the oil layer protective agent LXJ-1; 15 parts of the micro-nano plugging agent JS-G1; 15 parts of the amphiphilic pressure-bearing plugging agent AMP; 60 parts of the weighting agent limestone powder; 2 parts of the alkalinity regulator NaOH; and the rest is water. The total weight of all raw materials is 1000 parts.

[0028] In this embodiment, specifically during the Y1-2 lateral well drilling construction process, during the construction preparation: the upper part of the shale well section was first drilled with a zwitterionic polymer drilling fluid. After drilling to 200 m before the shale well section, the drilling fluid properties were adjusted, and an appropriate amount of weighting agent was added in time. The drilling fluid density was adjusted to 1.35 g / cm3 after circulating for 1-2 weeks. 3 The actual drilling density is adjusted to meet the formation pressure and wellbore safety requirements. At this time, the bentonite content is controlled at 30g / l by adding appropriate amount of water, and the viscosity is reduced to PV of 8-15mPa.s and YP of 3-5Pa, completing the drilling construction preparation before the shale well section.

[0029] System conversion: Add 0.2% drilling fluid inhibitor FA367 and 0.8% salt and high temperature resistant fluid loss reducer LV-PAC to the drilling fluid adjusted during construction preparation in the mass ratio of the total drilling fluid. After circulating the mud fluid for 2 weeks through the mud pump, add 7% potassium chloride in time and circulate it for another 2 weeks to convert it into a potassium chloride drilling fluid basic system.

[0030] Mixing adjustment: When drilling into mud shale, 1.5% by mass of low-fluorescence anti-collapse agent NFA-25 and 1.5% by mass of anti-collapse and fluid loss agent MFJ-1 are promptly added to the above-mentioned basic system; when drilling into mud shale with developed microcracks, 1.5% by mass of micro-nano plugging agent JS-G1 and 1.5% by mass of amphiphilic pressure-bearing plugging agent AMP are promptly added. In this embodiment, the following mixing adjustment effects are achieved: the plugging of mud shale with developed microcracks is highly targeted, the flow pattern is easy to control, the pressure-bearing plugging effect is good, and it is beneficial to the stability of the well wall.

[0031] Performance Maintenance: When drilling shale wells, replenish the wellbore with 0.15% by mass of low-fluorescence anti-collapse agent NFA-25 and 0.15% by mass of anti-collapse and fluid loss agent MFJ-1 every 100±1m of drilling progress. When drilling shale with developed microfractures, replenish the wellbore with 0.2% by mass of low-fluorescence anti-collapse agent NFA-25 and 0.2% by mass of anti-collapse and fluid loss agent MFJ-1, 0.2% by mass of micro-nano plugging agent JS-G1, and 0.2% by mass of amphiphilic pressure-bearing plugging agent AMP every 100±1m of drilling progress. The performance maintenance results achieved during this phase include: good rheology, low fluorescence levels, strong wall-building properties, high plugging and pressure-bearing capacity, and stable performance.

[0032] Reservoir protection: Add 1.5% oil layer protection agent LXJ-1 at one time 50m before entering the reservoir to maintain a relatively low implementation density, which is conducive to oil and gas discovery.

[0033] Completion preparation: During the completion phase, before electrical logging and casing running, the addition of environmentally friendly lubricant KD-21C was determined based on the need for wellbore lubrication and anti-sticking. The well was drilled to a depth of 4,068 meters without any wellbore instability, leakage, or collapse. During the drilling process, the filtration loss in the high-temperature, high-pressure section was 5.6 ml. Example

[0034] In this embodiment, during the drilling of the deep shale section of Well Y8 in Jiangsu Oilfield, according to the construction requirements of the target block formation stress, the raw material components and mass proportions are as follows: 30 parts of sodium bentonite; 3 parts of drilling fluid inhibitor FA367; 50 parts of potassium chloride powder; 15 parts of salt-resistant and high-temperature resistant fluid loss reducer LV-PAC; 10 parts of low-fluorescence anti-collapse agent NFA-25; 10 parts of anti-collapse fluid loss reducer MFJ-1; 10 parts of environmentally friendly lubricant KD-21C; 10 parts of oil layer protective agent LXJ-1; 10 parts of micro-nano plugging agent JS-G1; 10 parts of amphiphilic pressure-bearing plugging agent AMP; 60 parts of weighting agent limestone powder; 4 parts of alkalinity regulator NaOH; and the remainder is water. The total weight of all raw materials is 1000 parts.

[0035] During the drilling process of Well Y8, the drilling fluid of this embodiment was first used in the upper part of the shale section during the construction preparation. After drilling to 300 m before the shale section, the drilling fluid properties were adjusted and an appropriate amount of weighting agent was added in time. The fluid was circulated for 1 to 2 weeks to adjust its density to 1.35 g / cm 3 The actual drilling density meets the formation pressure and wellbore safety requirements. At this time, the bentonite content is controlled at 20g / l by adding appropriate amount of water, the viscosity is reduced to PV of 8-15mPa.s and YP of 3-5Pa, completing the drilling construction preparation before the mudstone well section.

[0036] System conversion: Add 0.3% by mass of drilling fluid inhibitor FA367 and 1.5% by mass of salt-resistant and high-temperature resistant fluid loss reducer LV-PAC to the drilling fluid adjusted during construction preparation according to the mass proportion of the total drilling fluid. After circulating the mud fluid for 2 weeks through a mud pump, add 5% by mass of potassium chloride in time and circulate it for another 2 weeks to convert it into a potassium chloride drilling fluid basic system.

[0037] Mixing adjustment: When drilling into mud shale, 1.0% low-fluorescence anti-collapse agent NFA-25 and 1.0% by mass of anti-collapse and fluid loss agent MFJ-1 are promptly added to the above-mentioned basic system; when drilling into mud shale with developed microcracks, 1.0% by mass of micro-nano plugging agent JS-G1 and 1% by mass of amphiphilic pressure-bearing plugging agent AMP are promptly added. During the implementation process, the plugging of the mud shale section with developed microcracks is highly targeted, the flow pattern is easy to control, and the pressure-bearing plugging effect is good, which is conducive to well wall stability.

[0038] Performance Maintenance: When drilling shale wells, replenish the wellbore with 0.2% low-fluorescence anti-collapse agent NFA-25 and 0.2% by weight of anti-collapse and fluid loss agent MFJ-1 every 100±1m of drilling progress. When drilling shale with developed microfractures, replenish the wellbore with 0.3% by weight of low-fluorescence anti-collapse agent NFA-25 and 0.3% by weight of anti-collapse and fluid loss agent MFJ-1, 0.3% by weight of micro-nano plugging agent JS-G1, and 0.3% by weight of amphiphilic pressure-bearing plugging agent AMP every 100±1m of drilling progress. The performance maintenance results achieved during this phase include: good rheology, low fluorescence levels, strong wall-building properties, high plugging and pressure-bearing capacity, and stable performance.

[0039] Reservoir protection: 50m before entering the reservoir, add 1% by mass of oil layer protection agent LXJ-1 at one time to maintain a relatively low implementation density, which is conducive to oil and gas discovery.

[0040] Completion preparation: During the completion phase, before electrical logging and casing running, the addition of environmentally friendly lubricant KD-21C was determined based on the need for wellbore lubrication and anti-sticking. The well was drilled to a depth of 4,169 meters without experiencing wellbore instability, leakage, or collapse. During the drilling process, the filtration loss in the high-temperature, high-pressure section was 5.4 ml. Example

[0041] In this embodiment, during the drilling of the deep shale section of the Y501 well in Jiangsu Oilfield, according to the construction requirements of the formation stress of the target block, the raw material components and mass proportions are as follows: 35 parts of sodium bentonite; 2.5 parts of drilling fluid inhibitor FA367; 60 parts of potassium chloride powder; 12 parts of salt-resistant and high-temperature resistant fluid loss reducer LV-PAC; 12 parts of low-fluorescence anti-collapse agent NFA-25; 12 parts of anti-collapse fluid loss reducer MFJ-1; 20 parts of environmentally friendly lubricant KD-21C; 12 parts of oil layer protective agent LXJ-1; 12 parts of micro-nano plugging agent JS-G1; 12 parts of amphiphilic pressure-bearing plugging agent AMP; 60 parts of weighting agent limestone powder; 3 parts of alkalinity regulator NaOH; and the rest is water. The total weight of all raw materials is 1000 parts.

[0042] During the drilling process of Well Y1-8, during the construction preparation stage, the drilling fluid of this embodiment was first used in the upper part of the shale section. After drilling to 300 m before the shale section, the drilling fluid properties were adjusted. Under the premise of meeting the formation pressure and wellbore safety requirements, an appropriate amount of weighting agent was added in time to adjust the drilling density to 1.36 g / cm 3 The actual drilling density is obtained. At this time, the bentonite content is controlled at 25g / l by adding appropriate amount of water, the viscosity is reduced to PV of 8-15mPa.s and YP of 3-5Pa, completing the drilling construction preparation before the mudstone well section.

[0043] System conversion: Add 0.25% by mass of drilling fluid inhibitor FA367 and 1.2% by mass of salt-resistant and high-temperature resistant fluid loss reducer LV-PAC to the drilling fluid adjusted during construction preparation according to the mass ratio of the total drilling fluid. After circulating the mud fluid for 2 weeks through the mud pump, add 6% by mass of potassium chloride in time and circulate it for another 2 weeks to convert it into a potassium chloride drilling fluid basic system.

[0044] Mixing adjustment: When drilling into mud shale, 1.2% low-fluorescence anti-collapse agent NFA-25 and 1.2% by mass of anti-collapse and fluid loss agent MFJ-1 are promptly added to the above-mentioned basic system; when drilling into mud shale with developed microcracks, 1.2% by mass of micro-nano plugging agent JS-G1 and 1.2% by mass of amphiphilic pressure-bearing plugging agent AMP are promptly added. During the implementation process, the plugging of the mud shale section with developed microcracks is highly targeted, the flow pattern is easy to control, and the pressure-bearing plugging effect is good, which is conducive to well wall stability.

[0045] Performance Maintenance: When drilling shale wells, replenish the wellbore with 0.15% low-fluorescence anti-collapse agent NFA-25 and 0.15% by weight anti-collapse and fluid loss agent MFJ-1 every 100±1m of drilling progress. When drilling shale with developed microfractures, replenish the wellbore with 0.2% by weight low-fluorescence anti-collapse agent NFA-25 and 0.2% by weight anti-collapse and fluid loss agent MFJ-1, 0.2% by weight micro-nano plugging agent JS-G1, and 0.2% by weight amphiphilic pressure-bearing plugging agent AMP every 100±1m of drilling progress. The performance maintenance results achieved during this phase include: good rheology, low fluorescence levels, strong wall-building properties, high plugging and pressure-bearing capacity, and stable performance.

[0046] Reservoir protection: 50m before entering the reservoir, add 1.2% by mass of oil layer protection agent LXJ-1 at one time to maintain a relatively low implementation density, which is conducive to oil and gas discovery.

[0047] Completion preparation: During the completion phase, before electrical logging and casing running, the addition of environmentally friendly lubricant KD-21C was determined based on the need for wellbore lubrication and anti-sticking. The well was drilled to a depth of 4,212 meters without experiencing wellbore instability, leakage, or collapse. During the drilling process, the filtration loss in the high-temperature, high-pressure section was 5.8 ml.

[0048] The drilling fluid system based on the present invention in the above-mentioned Examples 1-3 has good rheological properties, strong wall-forming properties, high sealing pressure bearing capacity, and low fluorescence level under high temperature conditions of 150°C. Under the condition of the same construction density in the same block, it extends the collapse cycle of the shale formation and can meet the requirements of safe drilling and oil and gas discovery in deep and long shale layers.

[0049] In addition, other wells in the nearby area were drilled with potassium ammonium based polymer drilling fluid in the prior art for shale formation drilling.3 Under these conditions, the high-temperature, high-pressure fluid loss reached 11.6 ml, and the shale wellbore instability caused resistance to completion electrical logging. The specific construction process is shown in the following comparative example.

[0050] Comparative Example 1

[0051] This comparative example was carried out according to the following construction plan when drilling the deep shale section of Well Y1-2 in Jiangsu Oilfield:

[0052] Preparation for the use of potassium ammonium-based polymer drilling fluid: Drilling was carried out in the upper part of the shale section using potassium polyacrylate polymer drilling fluid. 200 m into the shale section, solids control equipment was used to reduce the harmful solid phase in the drilling fluid. The bentonite content was controlled at 45-55 g / l by mass, the PV of the adhesive was 15-20 mPa.s, and the YP was 7-15 Pa.

[0053] System conversion of potassium ammonium based polymer drilling fluid: 1% ammonium salt fluid loss reducer and 0.2% polyamine inhibitor are added to the drilling fluid adjusted during construction preparation in the order of mass ratio. After circulating the mud pump for 2 weeks, it is converted into a potassium ammonium based drilling fluid basic system.

[0054] Potassium-ammonium polymer drilling fluid mix adjustment: When drilling into shale, add 1.5% modified asphalt and 1.5% polyol anti-slump agent to the base system according to the mass ratio. When drilling into shale with developed microcracks, add 2% ultrafine calcium carbonate and 1% anti-slump fluid loss agent. The effect of this drilling fluid mix adjustment: The plugging effect of shale with developed microcracks is not very targeted, the pressure-bearing plugging effect is weak, and the annular pressure loss is high during operation, which is not conducive to wellbore stability.

[0055] Potassium-ammonium polymer drilling fluid performance maintenance: When drilling in shale wells, supplement with 0.3% modified asphalt and 0.3% polyol anti-slump agent, by mass, every 100±1m of drilling progress. When drilling in shale with developed microfractures, supplement with 0.4% ultrafine calcium carbonate and 0.2% anti-slump fluid loss additive every 100±1m of drilling progress. Performance maintenance results of this drilling fluid: poor rheology, high fluorescence levels, high fluid loss at high temperature and high pressure, weak plugging and wall-building properties, and unstable performance.

[0056] Potassium ammonium based polymer drilling fluid for oil layer protection: before drilling into the reservoir, add 1% ultra-low permeability treatment agent and 2% ultra-fine calcium carbonate to prevent filtrate and solid phase from invading the oil layer.

[0057] Completion preparation of potassium ammonium based polymer drilling fluid: add % solid lubricant before electrical logging and casing running to improve the wellbore lubrication and anti-sticking performance.

[0058] In this embodiment, due to the instability of the shale wellbore during the drilling operation, the electrical measurement encountered resistance at 4065 m, and the high-temperature and high-pressure fluid loss reached 11.6 ml.

[0059] Comparative Example 2

[0060] This comparative example was carried out according to the following construction plan when drilling the deep shale section of Well Y1-3 in Jiangsu Oilfield:

[0061] Preparation for the use of potassium ammonium-based polymer drilling fluid: Drilling was carried out in the upper part of the shale section using potassium polyacrylate polymer drilling fluid. 300 m into the shale section, solids control equipment was used to reduce harmful solids in the drilling fluid. The bentonite content was controlled at 45-55 g / l by mass, the PV of the adhesive was 15-20 mPa.s, and the YP was 7-15 Pa.

[0062] System conversion of potassium ammonium based polymer drilling fluid: 1.5% ammonium salt filtrate reducer and 0.5% polyamine inhibitor were added to the drilling fluid adjusted during construction preparation in the order of mass ratio. After circulating the mud pump for 2 weeks, it was converted into a potassium ammonium based drilling fluid basic system.

[0063] Potassium-ammonium polymer drilling fluid mix adjustment: When drilling into shale, add 2% modified asphalt and 2% polyol anti-slump agent to the base system according to the mass ratio. When drilling into shale with developed microcracks, add 3% ultrafine calcium carbonate and 1.5% anti-slump fluid loss agent. The effect of this drilling fluid mix adjustment: The plugging effect of shale with developed microcracks is not very targeted, the pressure-bearing plugging effect is weak, and the annular pressure loss is high during operation, which is not conducive to wellbore stability.

[0064] Potassium-ammonium polymer drilling fluid performance maintenance: When drilling in shale wells, supplement with 0.4% modified asphalt and 0.4% polyol anti-slump agent, by mass, every 100±1m of drilling progress. When drilling in shale with developed microfractures, supplement with 0.6% ultrafine calcium carbonate and 0.3% anti-slump fluid loss additive every 100±1m of drilling progress. Performance maintenance results of this drilling fluid: poor rheology, high fluorescence level, high fluid loss at high temperature and high pressure, weak plugging and wall-building properties, and unstable performance.

[0065] Potassium ammonium based polymer drilling fluid for oil layer protection: before drilling to the reservoir, add 1.5% ultra-low permeability treatment agent and 3% ultra-fine calcium carbonate to prevent filtrate and solid phase from invading the oil layer.

[0066] Completion preparation of potassium ammonium based polymer drilling fluid: add 1.5% solid lubricant before electrical logging and casing running to improve the wellbore lubrication and anti-sticking performance.

[0067] In this example, due to the instability of the shale wellbore during the completion operation, the electrical logging encountered resistance at 3300 m and 3375 m, and the high-temperature and high-pressure fluid loss reached 11.2 ml.

[0068] In addition, during the drilling process of the above-mentioned embodiment and comparative example well sections, combined with the ground stress and formation pore pressure data of the target block, the absorption rate of the shale after soaking in drilling fluid, the mechanical properties and strength change law of the shale after absorption of drilling fluid were tested, and the change of the formation strength parameters over time was mainly considered. The VB program was used to quantitatively predict the wellbore collapse period, as shown in the following example: Figure 1 As shown, the experiment was conducted by comparing the potassium ammonium polymer drilling fluid with the drilling fluid of the present invention, and the calculation results are shown in FIG. Figure 1 and Figure 2 And Table 1-1.

[0069] Table 1 Comparison of field applications of potassium ammonium polymer drilling fluid and the drilling fluid of the present invention

[0070] From the above comparison results, it can be seen that the drilling fluid of the present invention prolongs the shale collapse period as the construction density increases, is more conducive to well wall stability, and meets the requirements of geological engineering integration.

Claims

1. A drilling fluid for extending the collapse period of shale, characterized in that: The invention comprises the following components by weight: sodium bentonite 3-4%; drilling fluid inhibitor 0.2-0.3%; potassium chloride 5-7%; salt-resistant and high-temperature resistant fluid loss reducer 0.8-1.5%; low-fluorescence anti-slump agent 1-1.5%; anti-slump fluid loss reducer 1-1.5%; environmentally friendly lubricant 1-3%; reservoir protective agent 1-1.5%; micro-nano plugging agent 1-1.5%; bi-philic pressure-bearing plugging agent 1-1.5%; weighting agent 1-6%; alkalinity regulator 2-4%; the remainder being water, totaling 100%; the low-fluorescence anti-slump agent is the environmentally friendly non-fluorescent anti-slump agent NFA-25; the micro-nano plugging agent is the environmentally friendly nano plugging agent JS-G1, which is prepared by mixing modified elastic resin, modified rosin, and a rigid plugging agent with a particle size of 100 nm-10 μm. The amphiphilic pressure-bearing plugging agent is an amphiphilic microsphere polymer material AMP composed of an oleophilic core and a hydrophilic shell; the anti-collapse and fluid loss agent is an anti-collapse and fluid loss agent MFJ-1.

2. The drilling fluid for extending the collapse period of shale according to claim 1, characterized in that: The drilling fluid inhibitor is a zwitterionic polymer FA367 with a molecular weight of 5 to 8 million.

3. The drilling fluid for extending the collapse period of shale according to claim 1, characterized in that: The salt-resistant and high-temperature-resistant fluid loss reducer is polyanionic cellulose LV-PAC.

4. The drilling fluid for extending the shale collapse period according to claim 1, characterized in that: The oil layer protective agent is ultra-low permeability treatment agent LXJ-1.

5. The drilling fluid for extending the collapse period of shale according to claim 1, characterized in that: The environmentally friendly lubricant is a water-based lubricant KD-21C or an environmentally friendly bio-lubricant JS-LUB; and the drilling fluid flow pattern regulator is a viscosity reducer MSO.

6. The drilling fluid for extending the collapse period of shale according to claim 1, characterized in that: The alkalinity regulator is NaOH; the weighting agent is limestone powder CaCO3 or BaSO4.

7. A construction method for a drilling fluid for extending the collapse period of shale according to any one of claims 1 to 6, characterized in that: The process includes the following: Construction preparation stage: Drilling is carried out in the upper part of the shale section using zwitterionic polymer drilling fluid. 200-300 m into the shale section, the drilling fluid properties are adjusted by adding 1%-6% weighting agent in a timely manner and circulating for 1-2 weeks to ensure that the density meets the formation pressure and wellbore safety requirements. The bentonite content is controlled at 20-30 g / l, and the viscosity is reduced to PV of 8-15 mPa.s and YP of 3-5 Pa. System conversion stage: Add 0.2% to 0.3% of drilling fluid inhibitor and 0.8% to 1.5% of salt and high temperature resistant fluid loss reducer to the drilling fluid adjusted in the construction preparation stage in order of mass proportion. After circulating the mud pump for 1 to 2 weeks, add 5% to 7% of potassium chloride in time and circulate it for another 1 to 2 weeks to convert it into a potassium chloride drilling fluid basic system. Mixing adjustment: When drilling into mud shale, promptly add 1% to 1.5% of low-fluorescence anti-collapse agent and 1% to 1.5% of anti-collapse and fluid loss agent according to the mass ratio to the basic system in the system conversion stage; when drilling into mud shale with developed microcracks, promptly add 1% to 1.5% of micro-nano plugging agent and 1% to 1.5% of bifacial pressure-bearing plugging agent; Performance maintenance: When drilling in shale wells, add 0.1% to 0.3% of low-fluorescence anti-collapse agent and 0.1% to 0.3% of anti-collapse and fluid loss agent in a timely manner for every 100±1m of drilling. When drilling in shale with developed microfractures, add 0.1% to 0.3% of fluorescent anti-collapse agent and 0.1% to 0.3% of anti-collapse and fluid loss agent in a timely manner for every 100±1m of drilling; 4% to 6% of micro-nano plugging agent and, in accordance with the mass ratio, bi-philic pressure-bearing plugging agent. Reservoir protection: Drill into the first 50m of the reservoir and add 1% to 1.5% of the oil layer protection agent at one time; Completion preparation: Before electrical logging and casing running, add 1% to 3% by weight of environmentally friendly lubricant to the drilling fluid according to the needs of wellbore lubrication and anti-sticking.

Images