--> Tight Gas Reservoir Characteristics and Proper Well Pattern Analysis: A Case Study in Ordos Basin

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Tight Gas Reservoir Characteristics and Proper Well Pattern Analysis: A Case Study in Ordos Basin


Block A lies west of Sulige in Ordos basin, and Sulige is a typical tight gas field, meanwhile, the biggest gas field in China. It has strong heterogeneity reservoirs with small isolated sand bodies, poor connectivity, and complex gas-water relationship. Its formation deposited in braided river sedimentary, and the effective sands are controlled by the distribution of point bar. The sands arrange in dots within the areas along the river. Sands are mainly isolated type with the thickness of 2~4 m, and the local superimposed sands can reach more than 6m. The reservoirs at block A, with a buried depth of 3200 ~ 3600 m, have an average porosity of 9.22% and an average permeability is of 0.8mD. Pore spaces types are dominated by lithic dissolved pore, and intercrystalline pore, with a few intergranular pore, intergranular dissolved pore and mixed base solution pores. Block A has been developed since 2008, and 354 wells have been drilled. However, cluster, vertical and horizontal wells are all adopted in Block A. Wells production performances differ greatly according to different geology condition and well pattern. For future drilling project, it is urgent to evaluate and compare the developing indexes including Estimate Ultimate Recovery(EUR), Original Gas in Place(OGIP) per well and Recovery Factor(RF) under different well pattern combining with the reservoir characteristic analysis.Based on analysis of the effective sand body size and their spreading directions from reservoir description, combining with interwell interference test at a infilled well pattern area, the developing effects are appraised for different well pattern through EUR, OGIP per well and RF in block A. Blasingame and AGRate Vs Time are recommended for estimation of OGIP per well and EUR through fitting with the production data including the casing pressure and the gas production rate. Parallelogram well pattern is advantageous to the balanced drilling, and formation pressure drop is more uniform to control a reasonable reservoir range. Vertical wells in parallelogram pattern of 500m*650m are recommended for a higher RE which can control more sands, and it is convenient for future well spacing adjusting. All these is essential and meaningful for more efficient developing and more reasonable well pattern plan of future drilling projects in this block.