How not to fail during the Reservoir Test for Low Permeability Formation: Case Study

Abstract

This paper presents The Exploration Well test solution under high pressure and low permeability. The work shows a new approach to the qualitative and quantitative description of the low permeability horizons by conducting the well testing before and after hydraulic fracturing. To provide a high degree of reliability, safety and efficiency in terms of time and quality of the received information the special combination of high-tech downhole tools was used. The previous experience of conducting the well testing in exploration wells at the Yamal-Nenets Autonomous Region showed difficulties due to the deep bedding, low permeability and abnormally high formation pressure. These types of formations require conducting the hydraulic fracturing to obtain the commercial flow at surface. During the well test after the hydraulic fracturing in a low-permeable reservoir usually it is not possible to achieve infinitely-acting radial flow regime within the allocated time which does not allow to estimate the actual horizontal permeability of the formation. To perform the complex well testing and effective hydraulic fracturing the combination of downhole tools, run-in hole on a tubing, including the perforating guns, packer, autonomous pressure gauges, downhole valves (tubing and circulation valves) controlled from the surface, was used. To assess the reservoir permeability the well testing was carried out with the inflow period without natural flow to the surface and pressure build-up shut-in at the bottom before creating the hydraulic fracture. As a result, the formation pressure, permeability and skin-factor are estimated. During this study, a multi-cycle valve controlled with a low-pressure impulse in the annulus played the major role in conducting several inflow periods, pressure build-ups with downhole shut-in and lifting the formation fluid to the surface by reverse circulating through the circulation valve. Before conducting the hydraulic fracturing, three mini-frac tests were carried out with injection of hydraulic fracturing fluid into the reservoir and recording the pressure fall-off with downhole shut-in. As a result of this period the fracture closure pressure, reservoir pressure, mobility and the effectiveness of fracturing fluid were estimated. After hydraulic fracturing, flowing periods were conducted to assess the well productivity with a created fracture. These well testing activities were carried out successfully in a safe manner and achieved reservoir evaluation objectives. This article discusses the unique experience and lessons learned from conducting the well testing with hydraulic fracturing using high-tech downhole equipment to achieve the successful results in low permeability reservoirs.