Technology Progress and Development of Coalbed Methane in Changqing Oilfield

Abstract

Changqing gas field is rich in coalbed methane resources, but lacks water resources. The high-intensity fracturing technology which was successfully used in other place needs lots of water and difficult to achieve economic benefits. Therefore, it is an urgent thing for Changqing Oilfield to develop a suitable, economic and efficient fracturing technology for coalbed methane development. Since 2023, focused on reducing costs and water and increasing production and efficiency, Changing Oilfield has conducted comprehensive research based on multiple basic theories such as rock mechanics testing, fracture propagation experiments, proppant transport laws in fracture net, and factors affecting horizontal well productivity. Synchronously, Changing Oilfield have also carried out serial comparative field tests with supporting fracture monitoring technology, gradually finalizing an economic scale fracturing technology for coalbed methane, the key points of this technology include few clusters in single stage, moderate scale, combined particle size, and alternating high and low-viscosity fluid injection. Based on fundamental research and field testing, we found that micro fractures and cleat are well-developed in coal rock, with a small difference in horizontal principal stress, this results in that coal crack by rock shear and slip, horizontal and vertical cleat opening successively, forming a three-dimensional network of intersecting fractures; Pumping rate and liquid viscosity are key factors affecting shape of hydraulic fracture, high pumping rate promotes non-planar fracture propagation, low viscosity fluid is easy to open the cleat and micro-fracture in coal bed, while high viscosity fluid helps reduce filtration and promote fracture be longer. Few clusters in single stage can concentrate energy and improve shape of fracture. When the sand addition intensity reaches 5-6t/m and the fluid intensity is 20-25m³/m, the length and conductivity of fracture, and EUR increase all slow down, initial production can reach 50000m3/km. The effective development of deep coal and rock coalbed methane has become an important resource guarantee for Changqing Oilfield.