Analysis of vertical permeability and its influence on CO2 EOR and storage in a carbonate reservoir

Analysis of vertical permeability and its influence on CO2 EOR and storage in a carbonate reservoir

Carbon dioxide

Enhanced recovery

Digital storage

Petroleum reservoirs

Geology

Buoyancy

Horizontal wells

Carbonation

Oil well flooding

Petroleum reservoir evaluation

Distribution functions

Flow simulation

The objective of this work is to improve the geostatistical understanding of vertical (bed-normal) permeability (kz) and its influence on reservoir performance during CO2 enhanced oil recovery (EOR) and storage. kz is scrutinized far less often than horizontal permeability (kx, ky) in most geological and reservoir modeling. However, our work indicates that it is equally important to understand kz characteristics to better evaluate its influence on CO2 EOR and storage performance prediction. We conducted this study on about 9,000 whole-core triaxial permeability (kx, ky, kz) measurements from 42 wells in the Seminole San Andres carbonate reservoir. We analyzed kz data, including heterogeneity, correlation, and sample sufficiency measures. We analyzed wells with the largest and smallest fractions of points with kz kmax = max(kx, ky), to explore geological factors that coincided with large kz. We quantified these geological effects through conditional probabilities on potential permeability barriers (e.g., stylolites). Every well had at least some whole-cores where kz kmax. This is a statistically justifiable result

only where Prob(kz kmax) is statistically different from 1/3 are core samples are non-isotropic. In conventional core data interpretation, however, modelers usually assume kz is less than kmax. For the well with the smallest fraction (11%) of cores where kz kmax, the cumulative distribution functions differ and coincides with the presence of stylolites. This is important for fluid flow when stylolites-bearing horizons are laterally extensive (100s of meters). We found that kz is about twice as variable as kx in many wells. This makes kz more difficult to interpret because it was (and usually is) heavily undersampled. To understand the influence of kz heterogeneity on CO2 flow, we built a series of flow simulation models that captured these geostatistical characteristics of permeability, while considering kz realizations, flow regimes (e.g., buoyant flow), CO2 injection strategies, and reservoir heterogeneity. CO2 flow simulations showed that, for viscous flow, assuming variable kx as per Seminole along with a constant kz/kx = 0.1 yields a close (within 0.5%) cumulative oil production to the simulation case with both kx and kz as uncorrelated variables. However, for buoyant flow, oil production differs by 10% (at 2.0 hydrocarbon pore volume HCPV of CO2 injected) between the two cases. Such flows could occur for small CO2 injection rates and long injection times, in interwell regions, and/or with vertically permeable conduits. Our geostatistical characterization demonstrates the controls on kz in a carbonate reservoir and how to alter conventional interpretation practices. This study can help CO2 EOR and storage operators refine injection development programs, particularly for reservoirs where buoyant flow exists. More broadly, the findings potentially apply to other similar subsurface buoyancy-driven flow displacements, including hydrogen storage, geothermal production, and aquifer CO2 sequestration. 2021, Society of Petroleum Engineers

2021-September

SPE Annual Technical Conference and Exhibition 2021, ATCE 2021, September 21, 2021 - September 23, 2021

2021

Ren, Bo

Jensen, Jerry

Lake, Larry

Male, Frank

conferencePaper

26386712

10.2118/205995-MS