A horizontal well drilling fluid for protecting coalbed methane reservoirs

Abstract

The invention relates to horizontal well drilling fluid for protecting a coal bed gas reservoir, belonging to the technical field of chemical agents of coal bed gas exploitation engineering. The horizontal well drilling fluid is characterized by comprising water, an anti-swelling agent, a discharge aiding agent, an anti-scaling agent and a flocculating agent; on the basis of the weight of 100% of water in percentage by weight, the anti-swelling agent accounts for 0.2-0.5%, the discharge aiding agent accounts for 0.05-0.1%, the anti-scaling agent accounts for 0.001-0.005%, and the flocculating agent accounts for 0.2-0.5%. The anti-swelling agent is industrial grade potassium chloride, and the discharge aiding agent is nonylphenol polyoxyethylene ether OP-10; the anti-scaling agent is 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP); the flocculating agent is liquid poly aluminum chloride (PAC). The horizontal well drilling fluid disclosed by the invention has appropriate degree of mineralization, can not form scales after being mixed with coal bed water, is low in surface tension and strong in interfacial activity, can flow back easily after invading a low-permeability coal bed, and has the characteristics of good compatibleness with the coal bed, strong flocculation ability, low cost and environment-friendliness.

Description

Technical field: [0001] The invention relates to a horizontal well drilling fluid for protecting coalbed methane reservoirs, and belongs to the technical field of engineering chemical agents for coalbed methane exploitation. Background technique: [0002] As my country's demand for energy is increasing, coalbed methane as one of the unconventional natural gas (coalbed methane, shale gas, tight sandstone gas and gas hydrate) is getting more and more attention. At present, the exploitation of coalbed methane in my country has been into a flourishing stage. [0003] Compared with foreign coalbed methane, my country's coalbed methane has its own special features, that is, the characteristics of low porosity and low permeability of coal seams, that is, low single well production. This low production characteristic also determines the low-cost strategy of my country's coalbed methane development. The use of horizontal wells for coalbed methane mining is becoming more and more wide...

AI Technical Summary

Problems solved by technology

[0004] However, clear water drilling fluid also has the following disadvantages: 1. The salinity of clear water is low, which can easily cause the hydration and expansion of clay minerals in the coal seam, thereby blocking the seepage channel of coalbed methane; 2. The clean water from the surface and the underground Coal seam water is incompatible and scaling phenomenon exists; 3. In the case of positive pressure difference drilling, the flowback ability of clean water intruded into low permeability coal seams is weak, which is extremely unfavorable for the drainage and mining of coalbed methane in the later stage; 4. The clear water flocculation ability is weak and cannot be The fine coal chips broken by the drill bit are removed in time, which will cause the fine coal chips to invade the coal seam and cause solid phase blockage

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