The value of a cementation exponent, usually obtained by rock and electricity experiments, significantly affects the calculation of water saturation, thickness of the hydrocarbon reservoir, and recovery rate. The determination of the cementation exponent for porous-media reservoirs has been a challenge because of the limited core sampling. A new method was proposed to determine the value of cementation exponent for complex triple-porosity media reservoirs in the work. Firstly, the work discussed the effects of fractures and nonconnected vugs on the cementation exponent of the reservoir as well as the calculation method of the cementation exponent of the dual-porosity media reservoir. Then, a new model for calculating the cementation exponent of triple-porosity media reservoirs was derived by combining the Maxwell-Garnett theory and series-parallel theory, which matched with the real physical-experiment data of rocks. The results showed that the fractures decreased the cementation exponent of the reservoir but the vugs increased. The mixture of matrix pores, fractures, and vugs made the value of the cementation exponent of the triple-porosity media reservoir vary around 2.0. The conductivity of the triple-porosity media reservoir was the external macroscopic expression of the microscopic conductive network. The new calculation model of the cementation exponent proposed in the work could reasonably predict the cementation exponent of the strongly inhomogeneous triple-porosity media reservoir.
Helium, a rare gas widely applied in high-tech fields, is a significant strategic resource in China. The foreign-trade dependence ratio of helium in China is 95%. The work reviewed the applications and market analysis of helium and reservoir modeling and distribution of helium in Changqing Gas Field as well as the helium extraction techniques from natural gases. According to the analysis of the component test and the dynamic monitoring of exploited gas wells and gas-gathering stations, the average helium content in Changqing Gas Field was 0.028%. Helium was rich in the northwest of Changqing Gas Field, but poor in the central and eastern regions. The helium volume contents in Qingyang Gas Field, Huanglong Gas Field, and the central, western, and southern regions of Sulige Gas Field have reached the industrial development standard. PetroChina performed the economic-feasibility evaluation and production-factor matching research on helium development and selected Changqing Gas Field as the demonstration for development. A large helium plant was established in Changqing Gas Field using the cryogenic method with/without membrane separation for helium extraction. Then, a helium development scheme was formulated and implemented to build the industry chain of helium in China. Changqing Gas Field is rich in helium resources. Developing helium has entered a strategic period with the technological advancement in extracting helium from natural gases and the increased prosperity of the international helium market. There are broad prospects and great benefits to exploiting helium resources in Changqing.
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