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Abstract
Fracability is a property that indicates how easy reservoir rocks can be fractured in hydraulic fracturing operations. It is a key parameter for fracturing design and evaluation. In order to utilize continuous logging data to predict fracability, synchronous tests of dynamic and static mechanical parameters of rocks under different confining pressures were conducted on 13 tight sandstone samples derived from the central Junggar Basin, China. A modified formula between dynamic and static mechanical parameters was established. Fracability of the tight reservoir in the Junggar Basin was then evaluated based on brittleness index, fracture toughness, and fracability index. The effectiveness of fracturing was analyzed combined with the oil testing curve after hydraulic fracturing. The results show that: (1) The distribution of oil-bearing formations in the studied area coincides well with stratum of higher fracability index. (2) The critical fracability index is determined to be 0.3, three formations are selected as fracturing candidates, and a thin mudstone interbed is identified in the oil-bearing formation. (3) Well testing curve verifies the reliability of the fracability evaluation method and the accuracy of the modified formula between dynamic and static mechanical parameters. This study provides useful information for improving fracturing operations of tight oil and gas reservoirs.
Highlights
With the increasing development of unconventional oil and gas, tight oil and gas has become a promising resource of oil and gas exploitation
The proposed fracability evaluation method was applied to the tight oil reservoir in the central Junggar Basin, China
It is found that the producing formations and the regions with higher fracability index have a higher degree of correlation
Summary
With the increasing development of unconventional oil and gas, tight oil and gas has become a promising resource of oil and gas exploitation. Mullen calculated elastic modulus and Poisson’s ratio using acoustic logging data (Rickman et al 2008) These methods for evaluating the brittleness of rock are to judge the degree of difficulty of fracture initiation. Neither brittleness index nor fracture toughness alone could fully evaluate the fracturing ability of rocks. Rock fracability is mostly determined using laboratory tests to measure the static mechanical parameters of rock. The dynamic mechanical parameters of rock can be obtained using standard logging data and the cost of measurement is much lower. Determining the relationship between dynamic and static mechanical parameters is a key to evaluate rock fracability using logging data, which is the primary goal of this study. Using the new formula, formation brittleness index, fracture toughness, and fracability index could be calculated. A plan for hydraulic fracturing was put forward based on the analysis
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