Key Technology for Infilling Adjustment of Well Pattern in Large Low Permeability Heterogeneous Gas Reservoirs: A Case Study in the M Gas Field

Comparing to sandstone gas reservoir, the low-permeability carbonate gas reservoir with has higher natural gas storage capacity and more economic benefits. It is an important area for exploration and development for tapping potential and maintaining stability. Taking M gas field, a large low-permeability carbonate gas reservoir in Ordos Basin, as an example, due to the gas reservoir enters the later stage of stable production, it faced serious problems of high reserves utilization (95%) and low gas recovery (25%). At this stage, the well pattern infilling adjustment is very urgent for the stable production and enhance gas recovery of the gas field. However, due to the widespread development of erosive trenches in M Gas Field with extremely strong heterogeneity, and after more than 20 years of development, it is very difficult to accurately describe and effectively utilize the remaining reserves scattered around the edges of the trenches and between wells. Therefore, this article focuses on two potential tapping areas, which are the edge of the trenches with low well control degree and between wells with high well control degree. First of all, it proposes a new method for describing the two remaining reserves by paleogeomorphic restoration based on paleogeomorphic characterization, and inter well formation pressure evaluation for low-permeability lithologic gas reservoirs. On this basis, it subdivides regional physical properties and development stage differences, with introducing effective permeability, infill timing, and economic benefit evaluation to establish identification curves for rapid deployment of infilled gas wells.Then key technologies for infilling and adjustment in the middle and late stages of development of large heterogeneous gas reservoirs have been established, which is clarified fundamental issues of “where, when, and how to add” for the gas field at this stage for the first time. The application results show that:1. The new palaeogeomorphic restoration method has improved the evaluation accuracy of the traditional trench potential tapping area from 76.3% to 88.3%, expanded the gas-bearing area of 540 km2, and fully implemented the trench potential tapping area; 2. The inter-well field pressure evaluation overcomes the problems of neglecting the pressure unbalance by the discharge radius method and long time consuming by the numerical simulation method. Besides, it successfully exploits the potential of two high energy value of inter-well in typical block which previous considering without infilling space; 3. Based on the key technology of infilling wells, 117 gas wells deployed in the trench area and 14 deployed in inter well area. It indicates good effect with 1.9 × 104 m3/d stable production in the initial period, which are predicted cumulative gas production increase is 85.2 × 108 m3 and increase gas recovery by 2.1%.