Study On A Bonding Strength Reinforcement Spacer For Coalbed Methane Well Cementing

There are abundant coal and coalbed methane(CBM)resources in China.China possesses the second largest coalbed methane reserves,which is 31.35 trillion cubic meters that can be exploited commercially.Coalbed methane is a new energy source and its exploration and development can meet the Chinese increasing demand for oil and gas resources.However,because of the high organic content and the developing and smooth joints surface,coalbed is loosely bonded to cement,resulting in a low bonding strength and poor quality of well cementing.In order to resolve the coalbed methane well cementing challenge,this study gave a new method to improve the wettability of coal surface and the well cementing quality,developed a surface modifier and created a novel bonding strength reinforcement spacer for coalbed methane well cementing.This new spacer can improve the cementing quality and ensure the successful stimulation treatments like fracturing in subsequent works.This study determined the wettability and surface microstructure of the coal core through the analysis of coal composition.It was found that the high content of C and O was the main reason for the poor wettability of coal surface.And this results in the poor bonding strength.In order to improve the wettability of coal surface,the effects of the silane coupling agent,latex and epoxy resin materials on the wettability of coal surface,the properties of cement slurry(such as rheological property,wait on cement time,compressive strength)and bonding strength between coal and cement were studied,and their corresponding mechanisms were also revealed through the analyses of coal surface morphology.According to the experimental results,the latex material can effectively improve the wettability of coal surface,changing the contact angle from 94.17°to almost 0°;improve the bonding strength between cement and coal for 55%growth;and have no detrimental effect on the comprehensive performances of the cement slurry.So it can be concluded that the latex bonding material is the most suitable as the surface modifier for coalbed,and its optimal addition is 8%.Based on the spacer for lost circulation prevention which had been developed in the"11th Five-Year"peroid and the surface modifier developed in above research,this study created a new bonding strength reinforcement spacer.This spacer is perfectly adequate for coalbed containing lots of joint and has the technical advantage of surface wettability modification and lost circulation prevention.This new spacer processes the characteristics of low density(1.04 g/cm~3),significant bonding strength improvement between coalbed and cement(70.79%)and good compatibility with cement slurry.The field application results of 5wells demonstrated that the new bonding strength reinforcement spacer does have the properties of lost circulation prevention and bonding strength improvement,which may effectively solve the lost circulation problem and improve cementing quality.This study will provide technical support for the development of coalbed methane in Diandong and Qianxi region.