A kind of clean drilling fluid for multi-branch horizontal well reservoir of coalbed methane and its preparation method

Abstract

The invention discloses clean drilling fluid used for a coal bed gas multi-branch horizontal well storage layer and a preparation method of the clean drilling fluid. The drilling fluid consists of the following materials in parts by weight: 100 parts of clear water, 0.5-1 part of a gelatinizing agent, 0.5-1 part of gelatinizing aid, and 0.1-0.2 part of a high temperature stabilizer, wherein the gelatinizing agent is composed of hexadecyl trimethyl ammonium bromide and cetyl pyridinium chloride monohydrate in a weight ratio of 4:1; the gelatinizing aid is composed of sodium salicylate and potassium chloride in a weight ratio of 1:1; the high temperature stabilizer is sodium thiosulfate. The drilling liquid does not use bentonite or polymer to improve viscosity, but uses micromolecule surfactant to form a micelle for increasing viscosity, is good in rock carrying capacity, quick and complete to break glue, and capable of guaranteeing a well hole to be clean while protecting the coal bed gas storage layer to the greatest extent, and reducing scouring of drilling fluid on well wall, so that drill blocking risks are lowered, and therefore, contradiction between the drilling safety and the storage layer protection in a drilling process of the existing coal bed gas multi-branch horizontal well is relieved to a certain extent.

Description

technical field [0001] The invention relates to a drilling fluid, in particular to a clean drilling fluid for multi-branched horizontal well reservoirs of coalbed methane and a preparation method thereof. Background technique [0002] As an unconventional gas resource, coalbed methane has been paid more and more attention. my country has abundant reserves of coalbed methane, so it is imperative to study the technology of coalbed methane exploration and development in depth. [0003] In the 1970s, research work on coalbed methane development began abroad, and a set of mature theories and mining techniques have been formed. However, the United States and other countries that are strong in coalbed methane exploration and development are mostly working on low-rank coalbed methane. Clear water is generally used as the drilling fluid for multi-branch horizontal wells completed. [0004] my country began to carry out research on coalbed methane in the 1990s. After 2005, the develo...

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Problems solved by technology

In recent years, my country's coalbed methane test wells mostly use multi-branch horizontal wells with open-hole completion, and the use of conventional oil and gas well drilling fluids has caused great damage to coalbed methane reservoirs, and often the gas production after drilling and completion is almost zero; because my country's coalbed methane development mainly Concentrate on high-rank coal. Compared with lower-rank coal, its strength is poor and it is easy to collapse. Using clean water as drilling fluid has poor lithology and serious erosion of the well wall. During drilling, the well wall is prone to instability and the rock Chips cannot be carried out in time, resulting in frequent drill stuck accidents

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