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CN-121991651-A - Borehole wall stable drilling fluid suitable for hard and brittle stratum and preparation method thereof

CN121991651ACN 121991651 ACN121991651 ACN 121991651ACN-121991651-A

Abstract

The invention provides a well wall stable drilling fluid suitable for a hard and brittle stratum and a preparation method thereof, wherein the drilling fluid comprises, by weight, 0.01-0.03% of soluble carbonate, 0.01-0.25% of alkaline regulator, 3.0-5.0% of bentonite, 1.0-3.0% of coating plugging agent, 1.0-4.0% of sulfonated phenolic resin, 0.1-0.5% of pressure resistance transmission agent, 5-15% of inhibitor, 4.0-8.0% of calcium carbonate, 1.0-3.0% of emulsified asphalt, 0.3-0.5% of xanthan gum and the balance of water. The invention has the technical characteristics of good plugging property and remarkable pressure transmission slowing. Compared with the conventional plugging anti-collapse drilling fluid system, the plugging performance is better, and the effective components in the drilling fluid can be rapidly coated and spread on cracks and cementing positions of the drilling fluid rock when the stratum is drilled, so that the pressure transmission and the hydration expansion pressure of clay minerals are rapidly reduced, the initial state of the stratum rock can be maximally maintained, and the well wall stability is realized.

Inventors

  • CHEN LEI
  • ZHAO HAIFENG
  • ZHANG XIAOPING
  • JIA JUN
  • QU BO
  • WANG JINGGUANG
  • ZHAO XIANGYANG
  • LIU WEI
  • DONG HONGWEI
  • DING LEI

Assignees

  • 中国石油天然气集团有限公司
  • 中国石油集团川庆钻探工程有限公司

Dates

Publication Date
20260508
Application Date
20241107

Claims (9)

  1. 1. A well wall stable drilling fluid suitable for hard and brittle formations is characterized by comprising, by weight, 0.01-0.03% of soluble carbonate, 0.01-0.25% of an alkaline regulator, 3.0-5.0% of bentonite, 1.0-3.0% of a coating plugging agent, 1.0-4.0% of a sulfonated phenolic resin, 0.1-0.5% of a pressure-resistant slow-transmitting agent, 5-15% of an inhibitor, 4.0-8.0% of calcium carbonate, 1.0-3.0% of emulsified asphalt, 0.3-0.5% of xanthan gum and the balance of water.
  2. 2. The wellbore wall stabilizing drilling fluid for hard and brittle stratum of claim 1, wherein the calcium carbonate is a mixture of 1250-mesh calcium carbonate and 325-mesh calcium carbonate, the weight percentage of the 1250-mesh calcium carbonate is 1-3%, and the weight percentage of the 325-mesh calcium carbonate is 3-5%.
  3. 3. The wellbore wall stabilizing drilling fluid of claim 1, wherein the inhibitor is potassium chloride or potassium formate.
  4. 4. A borehole wall stabilizing drilling fluid for hard and brittle formations as recited in claim 1 further comprising weighting materials, said weighting materials being added according to the density of the drilling fluid.
  5. 5. The well wall stable drilling fluid suitable for the hard and brittle stratum is characterized in that the coating plugging agent is formed by mixing acrylic polyurethane and acrylic polysiloxane according to a mass ratio of 1:1.
  6. 6. The well wall stable drilling fluid suitable for the hard and brittle stratum is characterized in that the pressure buffer transfer agent is formed by mixing polyether modified acrylate functional group dimethyl siloxane and an amino polymer according to a mass ratio of 1:3.
  7. 7. The wellbore wall stabilizing drilling fluid for hard and brittle stratum of claim 1, wherein the soluble carbonate is sodium carbonate or potassium carbonate.
  8. 8. The wellbore wall stabilizing drilling fluid for hard and brittle stratum of claim 6, wherein the amino polymer is polyether amine or polyethylene oxide, and the molecular weight of the amino polymer is not more than 5000.
  9. 9. The method for preparing the well wall stable drilling fluid suitable for the hard and brittle stratum according to claim 2, which is characterized by comprising the following steps: step 1), dissolving a formula amount of soluble carbonate and an alkaline regulator into a formula amount of water, and fully stirring until the soluble carbonate and the alkaline regulator are completely dissolved to obtain an alkaline solution; Step 2) adding bentonite with the formula amount into an alkaline solution, and stirring and hydrating for at least 24 hours to obtain a mixed solution; and 3) adding the xanthan gum, the coating plugging agent, the sulfonated phenolic resin, the pressure buffer transfer agent, the inhibitor, the 325-mesh calcium carbonate and the emulsified asphalt according to the formula amount into the mixed solution, and stirring for at least 1 hour to obtain the modified asphalt.

Description

Borehole wall stable drilling fluid suitable for hard and brittle stratum and preparation method thereof Technical Field The invention belongs to the technical field of water-based drilling fluid, and particularly relates to a well wall stable drilling fluid suitable for a hard and brittle stratum and a preparation method thereof. Background With the continuous progress of exploration and development towards deeper and more complex stratum, hard and brittle stratum such as hard and brittle carbonaceous shale is frequently encountered in drilling construction, and the collapse of the well wall of the hard and brittle shale in the drilling process is always a difficult problem faced by petroleum drilling due to the influence of multiple factors such as drilling fluid density, collapse prevention performance and stratum applicability. The weak structural surfaces such as bedding, cracks, micro-cracks and the like are ubiquitous under the action of higher ground stress, so that the well wall is easy to collapse and damage. The clay minerals of the hard and brittle stratum mainly comprise illite, the mass fraction of the clay is up to more than 40%, and the target interval is often drilled with different lithologies such as mudstone, black-gray mudstone, carbonaceous mudstone, coal rock and the like, the cementing effect among the different lithologies is poor, and the collapse risk of the well wall is high. The hard and brittle stratum has weaker cementing force in the vertical direction, the cementing force between layers is small, in the drilling process, stress release (unloading) and mechanical disturbance of a drilling tool are extremely easy to cause the cracking of well wall rocks, so that carbonaceous mudstones are flaked off along the bedding, the instability of the well wall is induced, and the collapse pressure PC is greatly increased. At present, the collapse of the well wall is mainly performed in the aspects of mechanics, chemistry, forced coupling and the like. The mechanical property is generally applied to the prediction of collapse pressure by a conventional elastic model, and reasonable drilling fluid density is adopted in the drilling process according to the prediction and field experience, so that the well wall is kept mechanically stable. The coal rock has small tensile strength and elasticity, and the too low density can cause the release of structural stress, so that the carbonaceous mudstone is cracked and collapsed along joints and cracks, the drilling fluid has too high density, and filtrate in the drilling fluid enters the carbonaceous mudstone to prop open the cracks so that the carbonaceous mudstone is peeled off. The precondition for chemical measures is the analysis of the mechanism around the collapsed sample, and the use of suitable inhibitors to inhibit hydration swelling of small amounts of potentially hydratable montmorillonite, swellable illite, etc. in hard brittle shale formations. The coupling aspect of the force is mainly to improve the blocking inhibition performance, good rheological property and the well cleaning capability of the drilling fluid. The Chinese patent CN 110551488A discloses a clay inhibitor for drilling fluid and a preparation method thereof, wherein the clay inhibitor is prepared from the following raw materials, by weight, 40-80 parts of nano-hydroxy aluminum, 30-60 parts of inorganic salt, 70-120 parts of polyacrylamide, 5-10 parts of ferrous chloride or ferrous sulfate, 50-100 parts of sulfonated nitro humic acid, 20-50 parts of lignosulfonate and 8-15 parts of potassium chlorate, and the preparation method comprises the steps of mixing and stirring the sulfonated nitro humic acid, the lignosulfonate, the potassium chlorate and the ferrous chloride or the ferrous sulfate, reacting for 1-1.5 h at 80-100 ℃, then adjusting the temperature to 35-40 ℃, adjusting the pH value to 9-11, then sequentially adding the nano-hydroxy aluminum and the inorganic salt, stirring for 20-30min, then adding polyacrylamide, and stirring for 2-3 h at 50-60 ℃ to prepare the clay inhibitor. The prepared clay inhibitor can be suitable for water-based drilling fluid, has strong ability of inhibiting hydration expansion of clay, and can alleviate the phenomenon of well wall instability. U.S. patent No. 5110484 provides an aluminum-based treatment for drilling fluids. The shale hydration dispersion can also be controlled by utilizing aluminum compounds synthesized by the reaction of sodium aluminate and syrup. To reduce the cost of production of such inhibitors, syrups are used as byproducts of sucrose extraction, containing sucrose, amino acids and amino acid salts/carboxylates. The non-reducing polysaccharide is hydrolyzed by inorganic acid to generate furfural and a degradation product with unobvious characteristics, and the degradation product is continuously reacted with alkali such as sodium aluminate to obtain a final product. The drilling fluid additive disclosed in t