Improving Horizontal Completions on Heterogeneous Tight Shales

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.

Fracture behavior of transversely isotropic rocks with discrete weak interfaces

“…Transversely isotropic elastic constants (Equation ) can be obtained from the engineering elastic parameters. It can be shown that the stiffness constants are given by Suarez‐Rivera et al: with …”

Developing Guidelines for Selection of Appropriate Fracture Models in the Numerical Simulation of Well Performance Behavior for Liquid Rich Ultra-Low Permeability ULP Reservoirs

“…If there is no horizontal stress contrast, or the maximum horizontal stress is in the same direction of the natural fracture's strike, hydraulic fractures will grow along the existing natural fracture orientation. Complex fracture networks will develop if there is a high horizontal stress contrast and the maximum horizontal stress is normal to the natural fracture strike (Suarez-Rivera et al 2013). Less brittle, soft shales aremore difficult to create large, conductive networks (Warpinski et al 2009).…”

Effect of material anisotropy on time-dependent wellbore stability

“…The mechanical properties for the TI rock are data published by Suarez-Rivera et al 23 We can assume an isotropic rock by using the mechanical properties measured in the x-direction of the TI rock as follows: E ¼44.68 GPa, v ¼ 0.283. Using the isotropic mechanical properties, one can calculate the isotropic linear elastic solution given by Jaeger et al 24 Figs.…”

“…The used data published by Suarez-Rivera et al 23 presented poroelastic example in Section 5 using the anisotropy ratios 1, 2 and 3. An anisotropy ratio of 1 corresponds to the isotropic rock model.…”

“…The strength parameters were not provided by Suarez-Rivera et al 23 and are assumed as follows: T o ¼1.0 MPa, S o ¼5.0 MPa, f ϕ ¼ 25 degrees, S ow ¼4 MPa and fw ϕ ¼20°, where T o is the rock tensile strength. Using these strength parameters, the abovementioned failure criteria were utilized to assess the borehole shear failure.…”