Abstract

Production from nanodarcy-range permeability shale formations requires extensive hydraulic fracturing, large volumes of water, and close-spaced wells. The current trend, which includes increasing lateral lengths, increasing the number of perforation stages, and increasing the volume of water and proppants pumped, is unsustainable. Comparing calculations of the possible surface area created during fracturing versus production results indicate that a large portion of the surface area is ineffective to production, resulting in ineffective use of resources and increased costs. This paper describes the fundamental understanding required to improve the efficiency of horizontal completions in oil- and gas-producing shales. Using extensive laboratory characterization of mechanical properties on core, core/log integration, and continuous mapping of these properties by logging-while-drilling (LWD) methods along the horizontal wellbore, appropriate guidelines are defined for effective perforation and fracturing to improve the efficiency and sustainability of horizontal completions. The objective of the study is to improve completion design and horizontal well completions efficiency. This objective is achieved by adequate selection of perforation intervals based on understanding the relevant physical processes and adequate rock characterization. Two reservoir regions, the near-wellbore and the far-wellbore, are defined and essential to completion design. Conditions at the far-wellbore region, which define the extent of the surface area in contact with the reservoir, are fundamental to well productivity. However, these conditions are often poorly understood. The near-wellbore region is the choking point to production, provided that ideal far-wellbore conditions exist. Properties along the near-wellbore region can be measured and are better understood. In this paper, these properties are used to minimize the near-wellbore choking effect by evaluating rock types that maximize near-wellbore fracture width, minimize breakdown pressures, and reduce the potential of solids production during the initial drawdown. The result is a nonsubjective and consistent methodology that defines the variability in near-well fracture performance along wellbores and allows selecting perforation stages based on measured or inferred rock properties (from LWD or drill cuttings analysis). Finally, the method that will be described provides a means for monitoring and comparing consistency between the predicted values and measured results by comparing the results to actual production data. The results of this study show the need to better understand the far-wellbore conditions as well as the near-wellbore conditions when making inferences about well production.

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