Research on Well Test Interpretation Model forUnconventional Tight Oil and Gas Reservoirs

Abstract

Unconventional energy resources have been characterized as those with large scale geometry and reserve, poor reservoir quality, which are difficult to evaluate and to apply the traditional techniques to develop for economic production. Unconventional oil and gas migration and flow mechanism dominate its exploration and development mode, which potentials are largely formation controlled. Very often, formation stimulation in unlocking the reservoir potential, such as fracturing technique is the key to develop unconventional reservoirs, such as the shale oil and gas, as well as the tight gas reservoirs. The state-of-art technology for tight oil and gas development is through long horizontal well with multi-stage fracturing. Presented in this study, based on the thorough study of unconventional reservoirs matrix and fracture seepage mechanism, and considering the finite conductivity and infinite conductivity fractures; as well as the parameters such as fracturing completely penetrating or partially penetrating; perforation in the fractures and between fractures, fracture half length, fracture dipping, fracture spacing etc., the multi-stage fracturing horizontal well test interpretation models are established. The model takes into account broader factors and wide field application conditions, therefore, more robust than other published fractured horizontal well test models. The current model for well test interpretation was solved using modern mathematical analysis methods. The type curves of multistage fracturing horizontal wells were generated. These type curves reflect the reservoir dynamic responses including those due to the main flow stage; the seepage flow characteristics of each stage, as well as the number of fractures, fracture half length, fracture conductivity, fracture inclination angle and other response characteristics. These type curves were then used by type curve matching methods to the well testing data from a field case, to calculate the reservoir and fracture parameters. The field application and case study have shown that the developed well testing model can meet the actual production evaluation requirements, and the results are in good agreement with those published for unconventional tight oil and gas reservoir evaluation. Keywords: unconventional, multi-stage fracturing, horizontal well, interpretation model, well test interpretation