Abstract
Construction of oil and gas wells at offshore fields often involves high formation pressure and the presence of swellable clay rocks in the section. In addition, productivity preservation is also an important aspect. For this purpose, it is necessary to reduce the solids content of the drilling mud. The purpose of this work is to develop, improve, and study compositions of weighted drilling muds with low content of solids, on the basis of organic salts of alkali metals and polymers for the construction of wells prone to rock swelling and/or cavings, as well as drilling fluids for drilling-in the formation. In order to achieve the set goal the following is required: Analysis of existing drilling muds of higher density for drilling wells in unstable rock intervals and for drilling in the productive formation; analysis of experience in using drilling systems on the formic acid salts base and substantiation of requirements for flushing fluids during well construction; development and investigation of drilling mud compositions on the formate base; and the evaluation of inhibiting effect of systems containing organic salts, polymer reagents, and calcium carbonate on clay samples. The developed drilling mud is characterized by a high inhibiting ability that allows minimized mud-weighting by the natural solid phase. This reduces the volume of prepared mud and facilitates the regulation of its properties by reducing the dispersion of drilled cuttings; it eliminates problems related to hydration and the swelling of active clay rocks; and stabilizes unstable argillites prone to caving. The low solids content, low filtration rates, and inhibitory nature of the mud allows high stability of the rheological properties of the mud, and preserves oil and gas reservoir productivity under conditions of elevated formation pressure.
Highlights
IntroductionIt is necessary to note the system’s ability to preserve the reservoir properties of the productive formation, ensure wellbore stability and integrity; include high zenith angles during the entire drilling interval until its casing; and higher drilling speeds through various sedimentary rocks, such as shale, clay shale, and limestone, etc
Numerous investigations prove that the problem of improving wellbore stability in unstable clay deposits can be solved by incorporating electrolytes and polymers into the solution used
Inhibiting the capacity of a flushing fluid refers to its ability to prevent or slow down deformation processes in the near-wellbore space
Summary
It is necessary to note the system’s ability to preserve the reservoir properties of the productive formation, ensure wellbore stability and integrity; include high zenith angles during the entire drilling interval until its casing; and higher drilling speeds through various sedimentary rocks, such as shale, clay shale, and limestone, etc. The drilling process is often complicated by the integrity of the borehole walls being compromised by unstable clay deposits (clays, shales, and mudstones). This can result in cavings, rockfalls, borehole constriction, and cavern formation, with cavings becoming more likely with the increase in depth and inclination angle. Worldwide experience in offshore drilling has shown that such actions do not fully exclude borehole stability disruption [2]
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