Naval Goel

Analytical modeling of gas recovery from in situ hydrates dissociation

Exploration activities around the world have confirmed that in situ hydrates are widely available in permafrost and oceanic sediments. These hydrocarbon deposits have stimulated worldwide efforts to understand gas production from hydrate dissociation in a porous media. This work is a contribution towards these efforts. The present study uses depressurization-driven in situ hydrate dissociation, incorporates decomposition kinetics into the radial diffusivity equation, and develops a model to predict the performance of naturally occurring hydrates. The proposed model is simple yet useful and it does not require any empirical correlation. The model-predicted performance compares well with the published experimental studies on the hydrate dissociation in porous media.

Correlating viscoelastic measurements of fracturing fluid to particles suspension and solids transport

An experimental study was performed to understand the relationship between fluid characteristics and its solids transport and sand suspension capabilities. In this study, borate crosslinked guar gels were prepared at three different pHs. The linear guar was crosslinked with borate crosslinker at concentrations from zero to the values where the gel exhibited phase separation at each pH. These gels were then characterized for viscoelastic properties and suspension settling velocities. At each pH, a crosslinker concentration was selected to evaluate the gels for their solids transport behavior in two large size slot models. The gels that satisfactorily transported solids through the slots had similar elastic moduli. The results show that the fluid elasticity, not viscosity, correlates with the solids transport capability of the crosslinked guar gels. Furthermore, the drag coefficients for the suspensions settling in the crosslinked gels prepared at three pHs were dissimilar, even at similar Weissenberg numbers. The drag on the suspensions settling in the viscoelastic guar gels was observed to be both more and less than the drag on the suspensions settling in the Newtonian fluids. Further work is needed to better understand these drag behaviors on the suspensions settling in viscoelastic guar gels.

Experimental investigation of proppant flowback phenomena using a large scale fracturing simulator

This paper evaluates the maximum flow rate before the sand production initiates while flowing back a reservoir after the hydraulic fracturing treatment. The experiments are performed in a high pressure slot which simulates a fracture. The slot is a parallel plate device, which is 7 ft high and 9 1/3 ft long with provisions for varying fracture gap width. The slot is filled with proppant to simulate a propped fracture, then, the closure pressure is applied with 12 actuators to simulate confining pressure on the proppant pack. Water is pumped into the slot to simulate flowing back of the fracturing fluid. The water flow rate is varied till the proppant pack destabilizes, and the sand production begins. The sand distribution is observed in the fracture with a vision system. The experimental results show that the critical water flowback rate decreases as the closure pressure increases, or when the fracture gap width increases. However, the sand-free maximum water flow rate increases as the sand size increases for a given fracture gap width. Lastly, the cumulative sand production decreases as the closure stress decreases at a particular flow rate. The visual observations of the proppant flowback phenomena show that the sand production initiates close to the perforation. After the initiation of the sand flow, continued pumping of the water results in sand production through a channel formed in the proppant pack.

A New Empirical Correlation to Predict Apparent Viscosity of Borate-Crosslinked Guar Gel in Hydraulic Fractures

Successful design and completion of the hydraulic fracturing treatments depend on accurate estimation of fracturing fluid viscosity under in-situ conditions. However, the viscosity of the widely used borate-crosslinked guar gel is extremely difficult to measure due to its dependence on temperature, wellbore shear pre-conditioning, fracture shear rate, and pH. Furthermore, these properties require that the fluid mixing, pumping, and characterization to be performed under representative field conditions. Because of these complexities, there is no reliable correlation available in the literature to relate borate-crosslinked guar gel viscosity with its dependent properties. Therefore, in the present study, borate-crosslinked guar gel rheology measurements, obtained with a field scale High Pressure Simulator (HPS), are used to develop a correlation. The empirical correlation is developed on the basis of method of reduced variables, whereby shear stress-shear rate data at different temperatures are combined into one curve at a reference temperature T o . Present study extends this method to include the effect of shear history on the rheology of guar polymer crosslinked with borate ions. In the paper, this technique is used to generate master curves of reduced apparent viscosity-shear rate for borate-crosslinked guar at each pH. Furthermore, the developed empirical equations relate apparent viscosity of crosslinked guar to fluid temperature, shear history and shear rate. The developed correlation is presented in a simple form. The correlation will be helpful for comparison of model calculated values with the laboratory measured viscosities, as the laboratory values are not supported by a field scale fluid characterization equipment.