Abstract
Multi-stage fracturing technique has been widely applied to tight oil/gas reservoirs. However, there still exists challenges to select the most applicable and economical well completion methods (WCMs) for a multi-stage fractured horizontal well (MFHW) in a tight oil reservoir. And, the theoretical methods used to select the best WCM for a particular MFHW are not fully investigated. At present, the existing models and methods are basically applied to conventional horizontal wells and the application of relevant models or methods in tight oil reservoirs are rarely involved.In this study, a comprehensive fuzzy evaluation system is developed to help engineers performing the optimal selection of WCMs for MFHWs in tight oil reservoirs. Firstly, the wellbore stability analysis is carried out to obtain the critical drawdown pressure which determines the availability of open-hole WCMs. Subsequently, a fuzzy evaluation model is proposed to preliminarily find out several potentially available WCMs for the target MFHW. The problems caused by non-quantification and fuzziness of effect factors are solved by membership functions. Then, on the basis of production decline analysis and the initial productivity prediction using a semi-analytical productivity model, the cumulative production in the future for the target MFHW using different candidate WCMs (fuzzy evaluation results) are predicted respectively. And an economic evaluation model is proposed to identify the most economic candidate WCM based on the cumulative production estimation results. Finally, the recommendation of the optimized WCM is performed with considering the obtained critical drawdown. With the help of the developed corresponding software, the proposed fuzzy system is applied along with two field applications in a tight oil reservoir. The results of optimal selection of WCMs for those two filed cases are validated by the field practices.
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