Study On Seepage Characteristics And Mining Rules Of Horizontal Wells In Different Types Of Reservoirs In Low Permeability Gas Reservoirs

Exploration and development of unconventional gas reservoirs has attracted more and more attention, natural gas reserves of low permeability gas reservoirs in unconventional gas account for a substantial proportion, and most of the low-permeability gas reservoirs in the state are to be exploited. Low permeability gas reservoirs have the characteristics of large reserves, development difficulties and low productivity. Horizontal well can enlarge drainage area, improve the flow characteristics of gas reservoirs and improve gas reservoir recovery. It has become the main way to develop low permeability gas reservoirs. Analysis of the dynamic changes of the production of horizontal well is the important work to study the development of low-permeability gas reservoir, find out the flow characteristics of low permeability gas reservoir is the theoretical foundation of the development law of horizontal wells, both of which have important significance.Through the combined method of laboratory experiments, numerical simulation and gas reservoir engineering, this paper takes XS gas reservoir as an example, to study the flow characteristics of different types of reservoirs in low permeability gas reservoirs and horizontal well development discipline. Firstly, this paper analyzed the geological characteristics of XS gas reservoir, classified and evaluated the reservoir, and introduced its development summary. Then, flow experiments of different types of reservoirs, including gas permeability testing experiment, CT scan, scanning electron microscopy and gas-water two-phase relative permeability tests were carried out. Based on the results of flow characteristics experiments, using numerical simulation method, the flow pattern changes of horizontal wells before and after fracturing and flow characteristics difference of horizontal wells and vertical wells before and after fracturing were studied. Also, the influences of pressure gradient, stress sensitivity, high-speed non-Darcy flow and slippage effect on fractured horizontal wells and flow capacity were simulated. Finally, gas reservoir engineering method was used to study the development laws of horizontal wells in low permeability gas reservoirs:the geological parameters of XS gas reservoir and production performance data of horizontal wells were counted, dynamic control reserves and control radius of horizontal wells were calculated, the production decline was analyzed, and the stable production capability of vertical wells and horizontal wells was compared and analyzed.Main conclusions and understanding achieved through the research:(1) Irreducible water saturation of low permeability gas reservoir is relatively high, the greater the absolute permeability of the core, the smaller its irreducible water saturation, the larger gas-water permeation area, and isotonic point upward shift more. (2) There are some micro-cracks or micro-pores in the cores which have good porosity and permeability. A small amount of micro-pores or micro-cracks present in the cores which have poor porosity and permeability, and clay minerals fill the void. (3) After fracturing horizontal wells, reservoir fluid flow tends to be more along the fracture, the fluid flow significantly faster, drainage area increases significantly. Under the same reservoir conditions, the relationship of the cumulative gas production among different well types is:fractured horizontal wells> unfractured horizontal wells> fractured vertical wells> unfractured vertical wells. (4)Kv/Kh has more influence on the production of unfractured horizontal wells. Taking start-up pressure gradient, stress sensitivity, high-speed non-Darcy flow into consideration, the production of fractured horizontal well decreases, drainage area narrows; the more intense the slippage effect, the higher the gas well productivity. (5) Gas wells drilled reservoirs better, higher productivity. The stable capacity of horizontal wells significantly is better than vertical wells, and the longer development time, the more obvious advantages of horizontal wells.