Perspective View on Gas Well Stimulations in Case of Complex Carbonate Reservoir

Abstract

Most modern challenges of gas field development are caused by an increase in complexity of geological structure, mainly associated with carbonate reservoirs. The studied field is characterized by the reservoir complexity, heterogeneity of reservoir properties both laterally and in section, the high impact of stratification factor and variability of rocks at micro scale. It significantly affects reliability of well productivity and field gas production prediction. For such fields, in order to reduce risks, it is necessary to identify the best technology for well stimulation, which allows achieving high gas recovery and economic efficiency. In this article, the five main criteria for the efficiency of such well operations are formulated. The authors present the results of application of basic well stimulation technology for carbonate reservoirs. It is acid treatment (acidizing) with various chemical compositions. The results of work on selective acidizing, both with the use of packer systems and with the use of chemical deviators, are described. On the next step a review of existing methods of well stimulation and selection of a new perspective technology, alternative to acid treatment, is performed. As an untested technology, the acid fracturing with flow deflectors is considered. Polymer spheres or complex polymer systems based on glass fibers and resins may be used as the deflectors. The purpose of acid fracturing is production enhancement by increasing of reservoir conductivity in the bottom-hole area, activation of non-flowing reservoir zones and reducing skin factor and D-factor values. An important task is to involve low permeable zones containing significant volume of gas in the production and preserve high productivity of high permeable zones. The selectivity effect is provided by flow deflectors. This technology is advisable to conduct on reservoirs that have several separated productive layers, when it is necessary to treat each layer. The authors identified main criteria for application of acid frac and selected appropriate wells. The design of acid fracturing was made with the use of a specialized software package. The impact of the reservoir features on fracture geometric parameters was studied. The final forecast of gas production increased. Economic efficiency was estimated with a use of the full-scale reservoir simulation model. The practical significance of the work is to generalize the experience of pilot projects carried out at the field, and to select a perspective technology for well stimulation in conditions of complex low permeable carbonates.