Drilling fluid

Abstract

FIELD: drilling oil and gas wells.SUBSTANCE: drilling fluid contains, by weight: bentonite clay powder 1.6-2.6; heat-and-salt-resistant modification of technical carboxymethyl cellulose “КМЦ-ТС” and acrylic polymer - reagent “ВПРГ” in a weight ratio of 3:1 0.65-1.0; sodium or potassium formate or a mixture thereof 2.0-15.0; calcium carbonate as a weighting agent 13.0-25.0; water - the rest.EFFECT: improvement in the filtration and inhibition characteristics of the drilling fluid, reduction in the negative impact of the drilling fluid on the filtration and capacity characteristics of productive formations during the initial opening of wells.2 cl, 3 tbl

Description

[0001] The invention relates to the field of drilling oil and gas wells, in particular to water-based drilling fluids for drilling and completing wells.

[0002] The combined use of polysaccharides with acrylic reagents and inorganic salts is known. For example, A.S. 1141109 (C 09 K 7 / 02, 23.02.85) describes the composition of a water-based polymer-clay mud containing CMC, polyacrylamide (PAA), and potassium chloride. The composition uses non-heat-resistant polymers, and its use is limited to drilling intervals with low bottomhole temperatures.

[0003] To increase the thermal stability of polysaccharides, the use of organic salts, such as formates, is recommended. According to document SPE 30498, potassium formate was used to increase the thermal stability of biopolymer systems comprising a biopolymer, PAC, calcium carbonate, and potassium formate to 150°C. However, in many cases, this thermal stability may be insufficient. Furthermore, a disadvantage of the solution was its high filtration rate.

[0004] The closest technical solution is a drilling mud (SU 1776689, 23.11.92) containing bentonite; 0.1 - 0.4% acrylic polymer (including hypane); 0.1 - 0.2% CMC; 0.05 - 0.2% KMOEC or OEC; 1.0 - 2.0% potassium chloride and up to 70 wt. % barite.

[0005] The disadvantages of the known technical solution are the unsatisfactory technological characteristics of the solution, namely:

[0006] - high filtration rate (filtration index value);

[0007] - low inhibitory activity;

[0008] - negative impact on reservoir permeability

[0009] The above mentioned disadvantages limit the scope of application of the known composition due to the ineffectiveness of its use in drilling clay deposits and opening productive formations.

[0010] The objective of the invention is to improve the composition of heat-resistant drilling mud.

[0011] The technical result of the invention is to improve the filtration and inhibition characteristics of the drilling mud, as well as to reduce the negative impact of the mud on the filtration and capacity characteristics of productive formations during the initial opening of wells.

[0012] The technical result is achieved in that the drilling mud contains bentonite clay powder, acrylic polymer, polysaccharide stabilizer carboxymethyl cellulose CMC, water-soluble salt, weighting agent and water, while it contains a heat-and-salt-resistant modification of technical carboxymethyl cellulose CMC-TS, as an acrylic polymer a water-soluble powder based on hydrolyzed polyacrylonitrile - acrylic reagent VPRG, and the mass ratio of CMC-TS: reagent VPRG is 3:1, as a water-soluble salt sodium or potassium formate or a mixture thereof, as a weighting agent calcium carbonate, with the following ratio of components, wt. %:

[0013] Bentonite clay powder 1,6 - 2,6 CMC-TS and HPRG reagent 0,65 - 1,0 Sodium or potassium formate or a mixture of both 2,0 - 15,0 Calcium carbonate 13,0 - 25,0 Water rest

[0014] To achieve the required density, the drilling fluid may additionally contain barite weighting agent.

[0015] Industrial materials are used to prepare drilling mud:

[0016] - highly colloidal bentonite clay powder of the PBMA, PBMB, PBB brands with a solution yield of at least 18 m 3 / T;

[0017] - heat-resistant salt modification of technical CMC - CMC-TS reagent with heat resistance of 160°C;

[0018] - acrylic reagent VPRG (dry hypane) - water-soluble powder based on hydrolyzed polyacrylonitrile;

[0019] - technical sodium formate with an active substance content of at least 98% and technical potassium formate with an active substance content of at least 96%.

[0020] Multi-fraction carbonate weighting agents or enriched natural chalk GOST 12085-88 grade MMS-2 can be used as calcium carbonate.

[0021] Depending on the mining and geological conditions of well drilling, the drilling fluid may additionally contain functional additives from a group including thinners, water repellents, defoamers, pH regulators, etc.

[0022] The preparation procedure for all proposed solutions and the prototype solution is the same. First, bentonite clay powder is dispersed in water. The resulting clay suspension is stabilized with polymers. After the polymers are completely dissolved, sodium formate or potassium formate, or a mixture of both, is added (in this case, sodium formate and potassium formate are used in equal quantities) (for the prototype solution, potassium chloride is used). The solution is then weighted to the required density using calcium carbonate and / or barite.

[0023] The proposed drilling fluid has a number of advantages compared to the prototype.

[0024] The combined use of the discovered polymer and organic salt composition enhances the mutual influence of these ingredients in the solution and provides a synergistic increase in the thermal stability of the composition, an improvement in the filtration rate and the inhibiting properties of the solution, which overall ensures a higher quality opening of productive formations than when using the prototype solution.

[0025] It is known that to maintain reservoir properties, a fluid must contain a minimum amount of insoluble materials, such as clay and barite. Furthermore, polymer fluid loss reducers (FLUs) used significantly impact reservoir productivity. For example, acrylic polymers are not recommended for use in well drilling and completion fluids. However, polysaccharides, including CMC-TS, are insufficiently thermally stable at high bottomhole temperatures (180°C), even in the presence of water-soluble salts. The resulting ratio of polysaccharide (CMC-TS) to acrylic (VPRG) polymers, 3:1, reduces the negative impact of acrylates on reservoir permeability and produces a stable, heat-resistant fluid with low FLU and excellent rheology.

[0026] Water-soluble salts—sodium formate, potassium formate, or their mixtures (in any ratio)—perform several functions simultaneously in the solution. As thermal stabilizers, they enhance the composition's thermal stability, inhibit swelling and dispersion of clay rocks, and can be used to increase the density of solutions by replacing weighting agents (barite).

[0027] The proposed drilling fluid was tested under laboratory conditions and compared with a prototype prepared according to the description. The composition of the fluid, as well as the composition of the prototype, are listed in Table 1.

[0028] Table 1

[0029] Name of the reagent Reagent content in the composition, mass % № 1 № 2 № 3 № 4 № 5 Prototype Bentonite clay powder 2,6 2,5 2,0 1,6 1,6 3,0 Filtration reducer, incl. 1,0 1,0 1,0 0,65 0,65 0,65 KMC-TS (KMC, KMOETS) 0,75 0,75 0,75 0,48 0,48 0,35 VPRG (hypan) 0,25 0,25 0,25 0,16 0,16 0,30 Sodium formate, Potassium formate, (potassium chloride) 2 - - - 5 - 10 - - 4,0 - - 7,5 7,5 - - - 1 Calcium carbonate 18 13 25 22 15 - Barite - - - 27 23 43 Water 76,4 78,5 62,0 44,75 44,75 52,35

[0030] *) The analogous reagents used in the preparation of the prototype solution are given in brackets.

[0031] The quality of the solutions was assessed using standard instruments and standard methods:

[0032] - density (r, g / cm 3 ), conditional viscosity, filtration, plastic viscosity (h пл , mPa hs), static (SNS 1 / 10 , dPa) and dynamic (t о , dPa) shear stress, pH before and after thermostatting at 180°C - in accordance with the “Methods for monitoring the parameters of drilling fluids” (RD 39-00147001-773-2004);

[0033] - inhibitory properties - according to the moisturizing capacity indicator (P о , cm / h) in accordance with RD 39-2-813-82;

[0034] - the degree of preservation of reservoir properties - according to the calculated OP indicator (the ratio of the actual productivity of the reservoir to the potential) in accordance with RD 39-0147001-742-92 "Methodology for a comprehensive assessment of the quality of opening productive formations, well completion and the selection of working fluids to improve the quality of opening formations."

[0035] The results are presented in Table 2.

[0036]

[0037] Analysis of the presented results shows that the proposed solution retains its filtration and structural-rheological characteristics after thermostatting at 180°C and significantly surpasses the prototype in terms of moisturizing capacity.

[0038] Table 3 shows the results of solution tests to evaluate their effect on maintaining reservoir permeability.

[0039] Table 3

[0040] Sample number OP value № 1 0,77 № 2 0,80 № 3 0,81 № 4 0,75 № 5 0,79 Prototype 0,56

[0041] The presented results allow us to evaluate the proposed solution as a more effective system in terms of preserving the natural permeability of the reservoir. Thus, the combination of the proposed features allows us to achieve the desired technical result.

Claims

1. A drilling mud containing bentonite clay powder, an acrylic polymer, a polysaccharide stabilizer carboxymethyl cellulose CMC, a water-soluble salt, a weighting agent and water, characterized in that it contains a heat-and-salt-resistant modification of technical carboxymethyl cellulose CMC-TS, as an acrylic polymer a water-soluble powder based on hydrolyzed polyacrylonitrile - an acrylic reagent VPRG, wherein the mass ratio of CMC-TS: VPRG reagent is 3:1, as a water-soluble salt sodium or potassium formate or a mixture thereof, as a weighting agent calcium carbonate in the following ratio of components, wt.%: Bentonite clay powder 1.6-2.6 Bentonite clay powder 1.6-2.6 CMC-TS and reagent VPRG0.65-1.0 CMC-TS and reagent VPRG0.65-1.0 Sodium or potassium formate or their mixture 2.0-15.0 Sodium or potassium formate or their mixture 2.0-15.0 Calcium carbonate 13.0-25.0 Calcium carbonate 13.0-25.0 Water Rest 2. The solution according to paragraph 1, characterized in that it additionally contains a barite weighting agent.

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