Film former used for coal-bed gas well drilling and preparation method thereof, drilling fluid and usage thereof

Abstract

The present invention relates to the well drilling field in the petroleum industry, particularly to film former used for coal-bed gas well drilling and preparation method thereof, drilling fluid and usage thereof. The preparation method of the film former includes: (1) controlling polycaprolactone diol and diisocyanate to have a first polymerization reaction in the presence of a polyurethane catalyst, to obtain a polyurethane prepolymer with two ends blocked by diisocyanate; (2) controlling the product of the first polymerization reaction to have a chain extension reaction with a polyalcohol; (3) controlling the product of the chain extension reaction and one part of hydroxyalkyl acrylate monomer to have an additive reaction, and then introducing the other part of hydroxyalkyl acrylate monomer and a styrene monomer, and emulsifying in water to obtain an emulsion; (4) mixing a radical initiator with the emulsion to have a second polymerization reaction.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to Chinese application no. 201710855400.4, filed on Sep. 20, 2017, entitled “film former used for coal-bed gas well drilling and preparation method thereof, drilling fluid and usage thereof”, which is specifically and entirely incorporated by reference.FIELD OF THE INVENTION[0002]The present invention relates to the well drilling field in the petroleum industry, particularly to a film former used for coal-bed gas well drilling, a preparation method thereof, a drilling fluid and a usage thereof.BACKGROUND OF THE INVENTION[0003]Coal-bed gas reservoir is quite different from ordinary sandstone or carbonate reservoir, and has characteristics such as high adsorbability, low permeability, and susceptibility to compression and fracture, etc. Owing to those characteristics, the coal bed is subjected to much more severe injuries than an ordinary reservoir in the coal-bed gas well drilling process, and the injuries ...

AI Technical Summary

Benefits of technology

The film former in this patent helps the drilling fluid system to form a good film on rock surfaces and protects the coal-bed gas reservoir.

Problems solved by technology

If the drilling / completion fluid is designed or used inappropriately in the well drilling / completion process, the liquid and solid in the drilling fluid may intrude into the oil reservoir and have physical and chemical reactions with clay and other minerals in the oil and gas layer.

Consequently, the permeability in the oil layer in the immediate vicinity of the well may be decreased severely, and the resistance against oil and gas flow towards the bottom of the well may be increased, resulting in reduced oil yield.

The major forms of reservoir damages happened in the coal-bed gas well drilling process include:(1) The drilling fluid is absorbed by the coal rocks, resulting in decreased permeability of the coal rocks;(2) The solid particles in the drilling fluid fill and plug the channels formed by fissures;(3) A polymer drilling fluid invades into the coal bed and causes clay flocculation and blockage under the adsorptive action of high molecular polymers, as well as clay swelling and blockage under the action of carboxyl hydration, and thereby results in decreased permeability of the coal bed;(4) The drilling fluid interacts with the formation water and generate solid precipitates, which result in blockage of channels formed by pores.

Production factors in the well drilling process, such as excessively high pressure of the drilling fluid column, reservoir bed soaked in the drilling fluid for an excessively long time, and excessively high pressure, etc., may also cause injuries to the coal bed.

Furthermore, well cementing operation and reservoir reformation measures taken to improve the yield (e.g., hydraulic fracturing) may also cause injuries to the coal-bed gas reservoir in different degree.