Using an Innovative Tool System to Estimate In-Situ Permeability and Pressure at Multiple Targets in a Monitoring Well in Permian Basin

Abstract

Permeability in tight sands and shale formations is a critical property that determines well performance, completion methods and field development strategies. Obtaining reliable permeability values in these reservoirs is challenging. Ultra low permeability and very strong stratification or heterogeneity in the formations require conducting long duration tests at multiple locations in a well to obtain a complete reservoir characterization. Because of these characteristics, existing tools or methods that work well for conventional reservoirs may not deliver reliable results. The objective of this work is to develop a technique that can provide permeability and pressure estimations as well as long term reservoir monitoring in multi-layer, tight formations. An innovative reservoir monitoring and testing tool system was developed and successfully applied to a dedicated reservoir observation well in Permian basin, Texas, USA. The tool system integrates the transient pressure tests for zonal formation property estimation and the long term reservoir performance monitoring in multi-layer, tight reservoirs. The tool string consists of 11 packers that isolated 10 major producing targets in tight sands and shale formations. Volume chambers and pressure sensors were installed in the string to create pressure pulses and record their corresponding responses from the isolated wellbore intervals for estimations of zonal in-situ permeability values and formation pressures. A fit-for-purpose transient pressure solution was also developed to analyze the data whenever the existing commercial software could not handle. Permeability and formation pressures in eight out of ten zones were obtained. The estimated permeability values have a range from tens of nano-Darcy in shale formations to hundreds of Micro-Darcy in tight sand layers, demonstrating the excellent flexibility and suitability of this technology to dynamic reservoir evaluation in tight and shale formations. After the impulse test, hydraulic fracturing operations in a near-by well induced a variety of pressure responses in different isolated intervals at the monitoring well. Strong correlations were obtained among the hydraulic fracturing induced pressure jumps, the zonal permeability values and depletions that were estimated from the earlier test. The results enable us to verify the estimated zonal permeability and formation pressures, pinpoint the height of fracture growth, calibrate fracture design models, improve well/fracture placement and construct a more representative reservoir model for field development optimization.