Slice-By-Slice Insights into the Wormhole Mechanism with Microscopic Precision Crucial to the Design of Efficient Acid Stimulation Treatments

Abstract We report the development of a novel coreflood testing quantitative evaluation which correlates data science and image processing of slice-by-slice microcore volume consumption with the differential pressure profile achieved during coreflood tests, facilitating the design of optimal treatments for acid stimulation. The outcome of microcore volume consumption studies obtained via high resolution CT scans are broadly applicable, enabling the design of customized acidizing stimulation treatments with minimal propensity for formation damage. The effects of physical testing conditions and fluid composition on microscopic wormhole profile development and core consumption volume using this original method are studied. We report detailed procedures of the coreflood tests, including carbonate core characterization, mineralogy, acid treatment specifications, and resultant wormhole profiles. Particularly, we accurately pinpoint differential pressure variations during the coreflood process in a stepwise manner via in-depth data and imaging analysis of high-resolution CT scans and correlate the changes to the corresponding fractional microcore volumes being consumed by the acid etching reaction at each incremental step. We present the differential pressure changes resulting from the high temperature acid etching reaction during the course of core flooding with corresponding microcore volume consumption along the core-axis in a slice-by-slice mode (with a precision of 0.02"/slice per CT scan). The acidizing fluids used in these tests were diligently formulated for effective modulation of the acid reaction rate with carbonate matrices at elevated temperatures. The resultant wormhole profiles are characterized and optimized under a given set of test parameters (temperature, differential pressure, acid fluid injection rate and treatment fluid composition) using the slice-by-slice technique. The effect of several acid packages on treatment efficiency based on microcore volume consumption is evaluated. In addition to 3D wormhole profiles, the kinetic insights of the acid etching reaction process from head-to-toe of the core are elucidated with microscopic precision, offering previously unavailable details, including the fractional contribution of each slice to the overall microcore volume consumed. By employing in-depth data and imaging analysis, a strong correlation between microcore volume consumption and the incremental differential pressure change is established. This important relationship provides critical light to the strategies leading to the most effective pore volume breakthrough performances for any given core that should be of critical importance when optimizing acid stimulation job designs. For the first time, stepwise changes in differential pressure profiles can be precisely correlated with corresponding microcore volumes consumed as an acid-coreflood etching process proceeds. This vigorous relationship, developed using an unprecedented methodology based on data science and imaging processing, offers potentially game-changing insights that can empower traditionally recommended acid coreflood testing practices, and assist in optimizing the design of reservoir acid stimulation treatments that minimize undesirable consequences of formation damage.