Characterization of Geomechanical Controls on Flow Behaviour in Tight Reservoirs

Abstract

This research details the characterization of geomechanical properties which is further utilized to scrutinize applications such as wellbore stability and the risk of sanding, and also to study the enhancement of fluid flow rates without compromising on sanding tendencies, ensuring safe production. This becomes even more critical for complex petroleum systems, particularly when the formation of interest is a predominantly unconventional reservoir characterized by subsurface heterogeneity and complexities. Elastic parameters (Poisson's ratio, Young’s modulus, shear modulus, bulk modulus) and strength parameters (cohesion, unconfined compressive strength, friction angle) were calculated using a basic well log suite and laboratory-based wave velocity measurement using the ultrasonic pulse wave velocity technique. Regression models were observed for the dynamic measurements obtained from a well log dataset and ultrasonic pulse measurement, which was further validated and correlated. Pore pressure is calculated using Eaton’s slowness which is based on Terzaghi’s principle. These parameters were applied in the poro-elastic strain model to compute the minimum horizontal stress gradient (Sh) and the maximum horizontal stress gradient (SH) of 0.78 psi/feet to 0.85 psi/feet and 0.89 psi/feet to 0.99 psi/feet, respectively. These parameters were further validated using Zoback’s stress polygon, reducing the range between the upper and lower bounds in estimating maximum horizontal stresses, thereby improving reliability. The ratio of minimum to maximum principal stress was calculated based on the frictional strength of pre-existing fractures and faults, which is affected by the underlying subsurface lithology. Mogi-Coulomb was utilized as a failure criterion to determine wellbore stability and to predict mud weight window ranging from 15.5-16 ppg for Raghavapuram shale and from 14.4-16.8 ppg for Nandigama sandstones has been ascertained as a safe window. This study uses quantified estimates of laboratory measured mineralogy and observation on the arrangements of these constituents and establishes a procedure to detect the wellbore failure. I thoroughly investigated overpressure generation in these formations, linked to clay diagenesis, compaction, and water expansion, using a velocity-density cross-plot and variation of porosity with increasing depth. Sanding tendencies in these formations were studied by analysing the critical drawdown pressure (CDDP), which depends on both critical bottom hole pressure and reservoir pore pressure at varying depletion rates. Wellbore with oriented perforations and formation with similar petrophysical properties were simulated using finite element modelling at field scenarios to calculate the fluid flow rates. The influence of oriented perforations, ranging from 0 to 360 degrees with a phase angle of 36 degrees, on fluid flow rates to minimize sanding tendencies was examined, and the critical fluid flow rates at drawdown were analysed. This thesis offers a novel approach by bridging the gap, combining laboratory-measured mineralogy and observations of constituent arrangements with numerical simulations and geomechanical parameters obtained from well log datasets in the studied formations.