Determination of Rock Compressibility in Unconsolidated Sand in Heavy and Extra-Heavy Oil Fields in Mexico

Abstract

Abstract Unconsolidated sands in heavy and extra-heavy oil fields in Mexico have significant potential that has not been fully evaluated yet. Thus, this paper examines petrophysics and geomechanical aspects with a view to estimating rock compressibility. This is important since determining this parameter from cores has proved to be difficult many times as the samples tend to collapse easily during laboratory experiments. The proposed method uses an empirical correlation for estimating Biot coefficient (Li et al., 2020) and more established geomechanical equations written in such a way as to allow the estimation of several types of compressibilities including: bulk compressibility, uniaxial bulk compressibility, pore compressibility, uniaxial pore compressibility, and pore compressibility under hydrostatic load. The data are loaded on a Pickett plot (1966, 1973) to demonstrate the value of pattern recognition. There are several intermediate results from calculations leading to the compressibilities mentioned above. These include process speed (ratio of permeability and porosity), pore throat aperture in microns at 35 percent cumulative pore volume (rp35), water saturation (Sw), mercury-air capillary pressure (pc), pore throat apertures (rp) at different water saturations, Biot coefficient (α), Poisson's ratio (PR), shear modulus (G), Young's modulus (YM), and fluid compressibility (cf). An important observation is that although use of the equations presented in the paper are straight forward and lead to quick calculation of all parameters mentioned above, it is likely that calculations from well logs without using pattern recognition may lead to uncertain results. The novelty of the paper is developing a methodology for calculating diverse types of rock compressibilities in unconsolidated sandstone reservoirs. Application of the methodology can lead to improved calculated recovery factors of unconsolidated sandstone reservoirs in heavy and extra-heavy oil fields in Mexico by at least 10%.