Theoretical and technological system for Highly efficient development of deep coalbed methane in the Eastern edge of Erdos Basin

Abstract

Aiming at the development problems of deep coal reservoirs, such as deep burial, low permeability and complex stress field, this paper clarifies that the resource enrichment conditions, effective fracturing volume, effective horizontal section length, and good reservoir conditions are the key factors for high productivity on the basis of summarizing the exploration and development practice of the Daning-Jixian Block in the past five years. Under the guidance of the theory of “artificial gas reservoir” development, a technical system for the efficient development of deep coalbed methane was preliminarily established as follows. ① According to the reservoir resource conditions, structural preservation conditions and engineering fracturing conditions, a total of 11 indicators in three categories established the geological-engineering “dessert” evaluation standards of deep coalbed methane. ② Based on the techniques such as microstructural characterization, multi-scale fracture prediction, and 3D geological model construction, the quantitative and visual characterization of all elements of “geology + engineering” of deep coal seam was achieved. ③ Based on the guiding idea of “geological small scale, three-dimensional seismic microscale, drill along the target, less adjustment and fast drilling”, a three-stage geological-engineering geo-steering technology with an excellent design of pre-drilling trajectory, precise target entry and post-target fine-tuning as the core was developed.④ The optimization design of the five-in-one well network based on “in-situ stress field, natural fracture field, artificial fracture field, well type and orientation, well network and well spacing” realized the maximization of resource utilization and the maximization of gas field recovery. ⑤ According to the occurrence characteristics, seepage mechanism and production characteristics of deep coalbed methane, a reasonable production capacity evaluation and EUR prediction technology based on the rate-transient analysis method, the empirical production decline method, the numerical simulation method, and the empirical analogy method was formed. ⑥ Following to the design principle of “four-in-one” precision fracturing section and “fracture staggering + differentiation between fracturing segments”, a large-scale volumetric fracturing technology aimed at constructing artificial gas reservoirs was proposed.⑦ According to the characteristics of gas-water variation in gas wells, the optimal control technology of drainage and production in different production stages through the whole life cycle of wells was put forwarded. ⑧ Combined with the current progress of AI technology, and the characteristics of deep coalbed methane development law, gathering and transportation, the technology of gathering, transportation and digital intelligence integrating geological, engineering, and ground aspects was explored. Under the guidance of this achievement, 29 horizontal wells that have been put into production，with an initial production of 5×104−16×104 m3/d, an average of 10.2×104 m3/d, and the daily gas production of the block has exceeded 3 million cubic meters, which has important guiding significance for accelerating the large-scale production of deep coalbed methane in the eastern margin of the Ordos basin. Also the study establishes a reference and standard for the efficient development of similar resources.

Keywords

• deep coalbed methane
• eastern margin of the ordos basin
• daning-jixian block
• theoretical and technological system for highly efficient development