RU2148702C1 - Method for drilling unstable clayey depositions in bore-hole - Google Patents

Abstract

FIELD: mining industry. SUBSTANCE: according to method, drilling of clayey depositions is effected with use of water-based drilling fluid containing reagent with binding properties. Used in function of reagent is water solution of water-soluble polyelectrolyte of cationic type of 0.3-1.0% concentration. Used in function of water-based drilling fluid is natural water suspension. Application of aforesaid method allows for avoiding complications connected with destruction of bore-hole walls. Well construction period is also reduced. EFFECT: higher efficiency.

Description

 The invention relates to the drilling of oil and gas wells in sections in which hydration-active unstable clay deposits are found, prone to destruction with the formation of caverns.

 A known method of posting unstable clay deposits of a section of a well (see the book by NG Sereda and EM Solovyov. Drilling oil and gas wells. - M.: Nedra, 1974, p. 226) by increasing the pressure on the walls of the well, t .e. by increasing the density of the wash solution.

Thus, the stability of Maykop clay with a moisture content of 12% can be increased by 1.9 times if the density of the clay solution is increased from 1300 to 1800 kg / m ³ .

 As you know, when using drilling fluids of such a density, the performance of the bit — penetration and mechanical drilling speed — sharply decreases.

 A known method of drilling wells in sections composed of unstable clay deposits (see AS No. 1641851, 6 C 09 K 7/02, published in BI No. 14, 91 under the name "Drilling mud"), including drilling clay sediments using a water-based drilling fluid with the addition of a reagent that improves the fastening properties (prototype).

 The disadvantage of this method is that for its implementation requires a drilling fluid of complex composition. In addition to the natural aqueous suspension, it contains clay, a stabilizing reagent, potassium containing a mineralizer, and a waste product from the production of extreme pressure additives for lubricating oils. The last reagent has fixing properties.

In addition, the reagent, which has fastening properties, also has a complex composition and contains Na ₂ SO ₄ , NaCl, CaS ₄ , Fe ₂ O ₃ , FeO, Na ₂ O and water.

 Without diminishing the dignity of the known method, we note that it requires expensive, scarce reagents, which leads to an increase in the cost of well construction. In addition, multicomponent complicates the technology of solution preparation.

 The aim of the present invention is to remedy these disadvantages.

 The goal is achieved by the described method, including drilling clay deposits using a drilling fluid, water-based, containing an additive reagent with fixing properties.

 New is that a natural aqueous suspension is used as a water-based drilling fluid, and a water-soluble cationic polyelectrolyte of the VPK-402 brand of 0.3-1% concentration is used as a reagent with fixing properties.

 At the filing date of the application from the patent and scientific and technical literature, the authors are not aware of the methods of the same purpose and with the same distinctive features, which allow to obtain a new positive effect, consisting in lowering the cost of the drilling fluid, in simplifying the technology of its preparation and, ultimately, in reducing the cost of well construction . In addition, the distinguishing features of the proposed method are not identical and equivalent in comparison with similar features of the known methods.

 The method is carried out in the following sequence.

 A well is drilled to the roof of unstable clay deposits of a section using water-based drilling fluids (industrial or sea water). As is known, as a result of the use of technical and sea water instead of clay mud, the penetration to the bit increases by 15-20%, and the mechanical penetration rate by 25-40%. However, water as a drilling fluid for drilling clay deposits is not recommended, since clay deposits swell, soften, forming caverns, in which drilled rock gradually accumulates, large particles of which are precipitated during forced circulation stops, causing wellbore development and other complications until the accident . Usually, in order to avoid complications in the interval of clay deposits, a cement bridge is installed, followed by drilling it after the cement has hardened. Therefore, according to the proposed method, in order to exclude the installation of a cement bridge before drilling clay deposits, a reagent with fastening properties is added to the natural aqueous suspension (EMU) - water-soluble cationic polyelectrolyte type VPK-402. VPK-402 in terms of quality meets the requirements of TU 6-05-2009-86, is produced by the Sterlitamak PA Kaustik in the form of a colorless to yellow liquid. VPK-402 polyelectrolyte is unlimitedly soluble in water, non-combustible, non-explosive, low toxicity, has no unpleasant odor.

 An aqueous solution of VPK-402 is prepared with a 0.3-1.0% concentration in mixing tanks by stirring. Adding VPK-402 to water less than 0.3% reduces the fastening properties of the solution, clay swelling is not excluded, thereby creating the risk of loss of stability of the well wall, and adding it more than 1.0% is not economically feasible.

 The VPK-402 aqueous solution in the above concentrations, in comparatively small quantities, does not lead to a noticeable increase in the density of water as a drilling fluid and does not adversely affect drilling performance, but rather improves, increasing the mechanical drilling speed.

If necessary, depending on the reservoir pressure, the VPK-402 aqueous solution can be weighted with mineralized water, including reservoir Devonian water or chloride solutions (CaCl ₂ , NaCl).

 Then, after sinking clay deposits, the drilling fluid prepared with VPK-402 aqueous solution is replaced with a natural aqueous suspension or ordinary clay drilling mud and the well continues to be drilled to the roof of the following clay deposits, if not, to the design depth.

 At the filing date of the application, the proposed method has successfully passed laboratory and field tests.

 Thus, according to laboratory studies, samples from Biklyan clay, Saraylyn and Kynov deposits after four hours of exposure in a 0.5% aqueous solution of VPK-402 under the influence of water are not destroyed within 10-12 days, whereas without preliminary strengthening they are destroyed within 2-4 hours.

 The method was tested in field conditions during the construction of well N 3509 of the Saraylinskoye field in accordance with the program and methodology approved by Tatneft.

 The results of field tests showed that in the test well complications were reduced by 25% than in the base wells of that field - wells. NN 3594, 3595 drilled by the same team that drilled the experimental well N 3509, due to which the construction time of the well was reduced by 3.5 days.

 The technical and economic advantage of the invention is as follows.

 Using the method can significantly reduce the cost of well construction, including time, since it does not require a drilling fluid of complex composition, therefore, it does not require a complicated technology for its preparation, scarce reagents with fixing properties. Complications during sinking of clay deposits are reduced by 25% or more, the performance of the bit is improved.

 The use of the method is promising and will reduce the cost and increase the technical and technological indicators of well construction.

Claims (1)

 A method of drilling unstable clay deposits of a well section, including drilling clay deposits using a water-based drilling fluid containing a reagent with fixing properties, characterized in that a natural aqueous suspension is used as a water-based drilling mud, and a reagent with fixing properties is used water-soluble cationic polyelectrolyte type VPK-402 0.3 -1% concentration.