Digital Revolution Provides a Step Change in Efficiency for Core Testing and Reservoir Upscaling for Acid Treatments

Abstract

Abstract This paper presents a digital stimulation workflow intended to revolutionize the area of tedious and core-destructive acidizing experiments. To adjust acid treatment design with respect to actual geology and lithology, several acidizing tests must be performed on cores taken from the reservoir of interest. However, complications related to core sampling and experimental uncertainties often make such tests infeasible, since the adjustment is based on "equivalent" data, which inevitably affects the treatment performance. A better result is achieved by supplementing laboratory tests with numerical simulation of reactive Darcy flow on digital avatars built using X-ray microtomography of real cores. Direct pore-scale simulations using high-resolution micromodels can help determine porosity, which in turn yields values for rock permeability, active surface area, and effective reaction rate. These data are then used to populate the standard core-size Darcy models used to simulate the rock dissolution at different injection rates. At the final step of the workflow, the obtained correlation of rock dissolution versus injection rate are used in advanced numerical simulators for well-scale modeling, in order to optimize the matrix-acidizing (MA) and acid-fracturing treatments. In this study, the concept was demonstrated by dissolving the limestone core in hydrochloric acid. The first phase of the workflow aims at digital expansion of the conventional laboratory work, which results in significant optimization of laboratory resources. Based on X-ray microtomography (microCT) scans of just two core samples and three laboratory filtration tests (one trial and two for the reference), by means of extensive cloud-based simulations, the authors were able to build two full-range pore-volume-to-breakthrough (PVBT) curves that are commonly used for treatment design. The second phase of the workflow involves reservoir-scale modeling and optimization of the acid treatment in an advanced digital simulator. A sensitivity study for the second-phase conceptual workflow was performed under typical well conditions in Middle Eastern basins to calculate volume and injection rates for optimum wormholing. Engineered design strategy going beyond conventional rule-of-thumb practices showed that significant production enhancement can be achieved while optimizing the acidizing project economics. Using a digital workflow makes it possible to optimize carbonate acidizing specifically for each well condition. Digital twins of the core samples and acid systems allows multiplying the number of filtration experiments by orders of magnitude, which significantly improves final data quality. Digital workflow is applicable to any carbonate reservoir using minimal core materials and lab resources.