Evaluation of Flow Units and Capillary Pressures of the Giant Chicontepec Tight Oil Paleochannel in Mexico and a Fresh Look at Drilling and Completions

The Chicontepec Paleochannel is a giant shaly sandstone reservoir(s) with volumes of OOIP ranging between 137 and 59 billion STB (Guzman, 2019), which has been equated recently to the Permian Basin. However, the oil recoveries are very small, ranging between 0.32 to 0.75% of the OOIP. Thus, the objective of this study is to evaluate flow units and capillary pressures of Chicontepec, as well as drilling and completion methods, with a view to improve the characterization of the reservoir(s) and, thus, oil recoveries.

Current cumulative oil production of Chicontepec is 440.38 million STB. Although it is a significant volume, it represents a very small percent recovery from the reservoir (0.32 to 0.75% of the OOIP). To help improving recovery, a method is developed for characterizing the tight Chicontepec paleochannel using flow units and capillary pressures. Like in the case of many tight unconventional reservoirs, the capillary pressures can go to very high values, reaching 55,000 psi in the Chicontepec case. Therefore, a special procedure is developed to generate a consistent interpretation of all the available capillary pressure curves for the entire range of pressures.

Results highlight the important oil recovery potential of the Chicontepec Paleochannel (Misantla-Tampico Basin), which has been equated recently to the Permian Basin in the United States and has been termed by Guzman (2022) "a premier super-basin in waiting." The assessment is supported by quantitative formation evaluation work performed by Gutierrez Oseguera and Aguilera (2022). Although natural fractures are present, most wells must be hydraulically fractured to achieve commercial success.

Process or delivery speed (the ratio of permeability and porosity) for the Chicontepec samples used in the capillary pressure experimental work range between 159.1 md and 0.17 md (porosity in the denominator is a fraction). Flow units show pore throat apertures (r_p35) ranging from less than 0.1 microns to about 4.5 microns. These values and flow units compare well with data available for prolific unconventional reservoirs such as the Cardium sandstone in Canada and the giant Permian Basin in the United States. The radius r_p35 refers to pore throat aperture at 35% cumulative pore volume.

The novelty of this study is the development of a consistent procedure for interpreting the entire range of pressures measured during mercury injection capillary pressures. Such pressures go up to 55,000 psi for the core samples considered in this study. The integration with flow units and formation evaluation suggests that the potential of the Chicontepec unconventional reservoirs can rival successful results obtained in the Cardium sandstone and the Permian Basin. Some ideas are advanced regarding drilling and completion for Chicontepec based on the results of the present study and production success in the Permian Basin.