published_or_final_version / Architecture / Master / Master of Landscape Architecture

published_or_final_version / Architecture / Master / Master of Landscape Architecture

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During production from gas condensate reservoirs, significant productivity loss occurs after the pressure near the production wells drops below the dew point of the hydrocarbon fluid. Several methods such as gas recycling, hydraulic fracturing and solvent injection have been tried to restore gas production rates after a decline in well productivity owing to condensate and/or water blocking. These methods of well stimulation offer only temporary productivity restoration and cannot always be used for a variety of reasons. Significant advances have been made during this study to develop and extend a chemical treatment to reduce the damage caused by liquid (condensate + water) blocking in gas condensate reservoirs. The chemical treatment alters the wettability of water-wet sandstone rocks to neutral wet, and thus reduces the residual liquid saturations and increases gas relative permeability. The treatment also increases the mobility and recovery of condensate from the reservoir. A nonionic polymeric fluoro-surfactant in a glycol-alcohol solvent mixture improved the gas and condensate relative permeabilities by a factor of about 2 on various outcrop and reservoir sandstone rocks. The improvement in relative permeability after chemical treatment was quantified by performing high pressure and high temperature coreflood experiments on outcrop and reservoir cores using synthetic gas mixtures at reservoir conditions. The durability of the chemical treatment has been tested by flowing a large volume of gas-condensate fluids for a long period of time. Solvents used to dissolve and deliver the surfactant play an important part in the treatment, especially in the presence of high water saturation or high salinity brine. A screening test based on phase behavior studies of treatment solutions and brines has been used to select appropriate mixtures of solvents based on reservoir conditions. The adsorption of the surfactant on the rock surface has been measured by measuring the concentration of the surfactant in the effluent. Wettability of treated and untreated reservoir rocks has been analyzed by measuring the USBM and Amott-Harvey wettability indices to evaluate the effect of chemical treatment on wettability. For the first time, chemical treatments have also been shown to remove the damage caused by water blocking in gas wells and for increasing the fracture conductivity and thus productivity of fractured gas-condensate wells. Core flood experiments done on propped fractures show significant improvement in gas and condensate relative permeability due to surface modification of proppants by chemical reatment. Relative permeability measurements have been done on sandstone and limestone cores over a wide range of conditions including high velocities typical of high rate gas wells and corresponding to both high capillary numbers and non-Darcy flow. A new approach has been presented to express relative permeability as a function three non-dimensionless terms; capillary number, modified Reynolds Number and PVT ratio. Numerical simulations using a compositional simulator have been done to better understand and design well treatments as a function of treatment volume and other parameters. Injection of treatment solution and chase gas and the flow back of solvents were simulated. These simulations show that chemical treatments have the potential to greatly increase production with relatively small treatment volumes since only the near-well region blocked by condensate and/or water needs to be treated.

Project Completion Report, OWRT Project No. A-091-ARIZ / Agreement No. 14-34-0001-8003 / Project Dates: October 1978 - September 1979 / Acknowledgement: The work upon which this report is based was supported by funds provided by the United States Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1978. / This report contains the results of a one year study to develop improved methods of evaporation control using wax impregnated foam. The foam used was expanded polystyrene and the wax used was paraffin with a 140° F melting point. The report tells of a pressure chamber that was used to wax impregnate sheets of expanded polystyrene. Based on tests made in the laboratory the pressure chamber was modified into a vacuum chamber. Problems were encountered getting the interior of the sheets impregnated using a vacuum. There was no way this problem could have been predicted based on the smaller laboratory models. The pressure method, however, was successfully used to impregnate up to 3 -inch thick sheets of expanded polystyrene. During the project it was found that the paraffin impregnated rafts worked very well until high temperatures, 100° F plus, are encountered Under dusty conditions. The heat causes the surface of the wax to get tacky, the dust darkens the otherwise white surface, which in turn captures more heat, and then more dust, etc. The high surface temperature caused an accelerated weathering of the material. Because of this, waxes with higher melting points were tried. Additional work is needed in this area as no satisfactory combinations were found. Two polyethylene copolymers with a melting point close to the 190° F destruction point of the expanded polystyrene were tested. This wax was too viscous for impregnation but provided a hard surface coating when the previously wax impregnated expanded polystyrene is dipped into the molten polyethylene wax. This dipping might be the best method for surface protection at low cost but additional testing is needed before trying the material out on a large scale. Progress was made in the development of wax impregnated lightweight concrete rafts. The wax impregnation of the lightweight raft solves the vapor penetration problem. This type of raft was found to resist removal by wind and weathered very well in the one year of testing. Connecting rafts with strips of sheet metal bonded to the expanded polystyrene was done on a small scale, and needs to be field tested. The PVC pipe C clamps work well on partially submerged rafts but need to be lengthened to interconnect wax impregnated rafts. Square wax impregnated rafts lx1 ft in size did not stay on a small test pond in high wind. Circles are presently being tried but additional testing is needed in this area before their reliability is known.

Research Project Technical Completion Report (A-109-Ariz.) For: United States Department of the Interior, Project Dates: 1981-1983, September 1, 1983. / The Research on which this project is based was financed in part by the U.S. Department of the Interior, as authorized by the Water Research and Development Act of 1978 (P.L. 95-467) / A liquid level interferometer has been built to measure changes in water level to an accuracy of /8. A novel magnetic suspension is used to position the floating retroreflector of a laser interferometer. Direction sensing is achieved by dual optical channels phased near quadrature by means of an absorbing beamsplitter. The interferometer (laser) has been used to measure very accurately the drop in water level of a lined reservoir. The drop in water level thus provides a precise method of measuring evaporation. It was found that this drop in water level essentially ceased when the relative humidity approached very closely or equaled 100 percent during early morning calm periods. This provides a method of determination of seepage loss. In an unlined reservoir during calm periods when the relative humidity is 100 percent any remaining drop in water level is due to seepage. The laser can measure this rate.

This project is a research into the effect of gas condensate damage in hydraulically fractured wells. It is the result of a problem encountered in producing a low permeability formation from a well in South Texas owned by the El Paso Production Company. The well was producing a gas condensate reservoir and questions were raised about how much drop in flowing bottomhole pressure below dewpoint would be appropriate. Condensate damage in the hydraulic fracture was expected to be of significant effect. Previous attempts to answer these questions have been from the perspective of a radial model. Condensate builds up in the reservoir as the reservoir pressure drops below the dewpoint pressure. As a result, the gas moving to the wellbore becomes leaner. With respect to the study by El-Banbi and McCain, the gas production rate may stabilize, or possibly increase, after the period of initial decline. This is controlled primarily by the condensate saturation near the wellbore. This current work has a totally different approach. The effects of reservoir depletion are minimized by introduction of an injector well with fluid composition the same as the original reservoir fluid. It also assumes an infinite conductivity hydraulic fracture and uses a linear model. During the research, gas condensate simulations were performed using a commercial simulator (CMG). The results of this research are a step forward in helping to improve the management of gas condensate reservoirs by understanding the mechanics of liquid build-up. It also provides methodology for quantifying the condensate damage that impairs linear flow of gas into the hydraulic fracture.

This research utilizes the imbibition experiments and X-ray tomography results for modeling fluid flow in naturally fractured reservoirs. Conventional dual porosity simulation requires large number of runs to quantify transfer function parameters for history matching purposes. In this study empirical transfer functions (ETF) are derived from imbibition experiments and this allows reduction in the uncertainness in modeling of transfer of fluids from the matrix to the fracture. The application of the ETF approach is applied in two phases. In the first phase, imbibition experiments are numerically solved using the diffusivity equation with different boundary conditions. Usually only the oil recovery in imbibition experiments is matched. But with the advent of X-ray CT, the spatial variation of the saturation can also be computed. The matching of this variation can lead to accurate reservoir characterization. In the second phase, the imbibition derived empirical transfer functions are used in developing a dual porosity reservoir simulator. The results from this study are compared with published results. The study reveals the impact of uncertainty in the transfer function parameters on the flow performance and reduces the computations to obtain transfer function required for dual porosity simulation.