State-of-the-Art in Coalbed Methane Drilling Fluids

Abstract

The production of methane from wet coalbeds is often associated with the production of significant amounts of water. While producing water is necessary to desorb the methane from the coal, the damage from the drilling fluids used is difficult to assess, because the gas production follows weeks to months after the well is drilled. Commonly asked questions include the following:• What are the important parameters for drilling an organic reservoir rock that is both the source and the trap for the methane?• Has the drilling fluid affected the gas production?• Are the cleats plugged? • Does the "filtercake" have an impact on the flow of water and gas?• Are stimulation techniques compatible with the drilling fluids used?This paper describes the development of a unique drilling fluid to drill coalbed methane wells with a special emphasis on horizontal applications. The fluid design incorporates products to match the delicate surface chemistry on the coal, a matting system to provide both borehole stability and minimize fluid losses to the cleats, and a breaker method of removing the matting system once drilling is completed. This paper also discusses how coal geology impacts drilling planning, drilling practices, the choice of drilling fluid, and completion/stimulation techniques for Upper Cretaceous Mannville-type coals drilled within the Western Canadian Sedimentary Basin. A focus on horizontal coalbed methane (CBM) wells is presented.Field results from three horizontal wells are discussed, two of which were drilled with the new drilling fluid system. The wells demonstrated exceptional stability in coal for lengths to 1000 m, controlled drilling rates and ease of running slotted liners. Methods for, and results of, placing the breaker in the horizontal wells are covered in depth.

CBM drilling technical parameter optimization methodology and software development: a case study of LUAN mining area

“…There are still many difficult problems to be solved in the coal and coalbed methane development. For example, drilling fluid leakage, roof damage and water inrush and coal and gas outburst (Baltoiu et al 2008, Ezeakacha & Salehi 2018, Balavi & Boluk 2018, Zeng et al 2017, Jia et al 2017, Geng et al 2017, Wang et al 2018. Drilling leakage, a common and frequent accident in CBM drilling practice of Luan mining area, China, seriously restricts the normal CBM drilling progress.…”

Experimental study on the influence of coal powders on the performance of water-based polymer drilling fluid

“…Barr (2009) introduced the guiding design principles of drilling fluids for CBM reservoirs, and thought it should be based on aspects such as nearby well data, reservoir characteristics, coal rank, drilling fluid rheology, shale rolling recovery experiment, and methylene blue content. Baltoiu et al (2008) designed a drilling fluid, which could keep the horizontal well stable and also reduce leak-age; it has been successfully used in two 1000 m long horizontal wells. Gentzis et al (2009) discovered that two treatment agents could form thin mud cakes on the surface of a coal rock with strong plugging capability, and they could duly maintain their stability, as well as reduce leak-age.…”

Drilling muds for coal deposits

“…Porosity is the basic parameter affecting the coal properties. The coal pore structure not only directly determines the gas adsorption and coal desorbability (Chakhmakhchev, 2007;Hadro and Wójcik, 2013;Baltoiu et al, 2016;Robbins et al, 2016;Li et al, 2018), but also impacts the interaction between the rock pores and the drilling fluid. Permeability is the second, not less important parameter and directly related to porosity, which is a decisive factor affecting the possibility to extract methane from the seams.…”

“…as a result of drainage and organic material shrinkage during the coalification. The type of maceral and coal quality are two most important factors, which determine the development of cracks and breaks in coal (Zhang et al, 2010;Zhao et al, 2012;Benguang et al, 2013;Baltoiu et al, 2016;Li et al, 2018).…”

“…Effective coal permeability decreases with the depth and with acting overburden stresses. Methane can exist as free gas in the network of cracks and fissures or as trapped gas adsorbed in the coal matrix or in the micropores structure (Chakhmakhchev, 2007;Moore, 2012;Baltoiu et al, 2016). Majority of methane resources exist in coal micropores.…”