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Collaborating Authors
Results
Experimental Study of Water Shut-Off by Wettability Alteration to Gas Wetness
Li, Kewen (China U. of Geosciences (Beijing)) | Yangtze, U.. (now with National Energy Administration, China) | Zhang, Haoping (now with National Energy Administration, China) | Peking, U.. (now with National Energy Administration, China)
Abstract Gas wells may suffer significant decline in gas production or even get killed because of the water invasion into production zones. Closing off the water producing zone may not be acceptable in many cases. In this study, the feasibility of reducing the water production in gas wells by changing the wettability of the gas zone from preferential water- to gas-wetness using fluorine carbon surfactant has been investigated experimentally. The basic mechanism was that the entry capillary pressure has to be overcome prior to water entering the gas zone. Naturally water can imbibe into gas zones spontaneously because the rock in gas zones is water wet, most probably. After the wettability alteration from water- to gas-wetness, water cannot enter into gas zones if the differential pressure is less than the entry capillary pressure and the water flux will be significantly reduced even if the differential pressure is greater than the entry capillary pressure. An artificially made, consolidated two-layer core model was used to conduct the study. The two layers had different permeability and the top layer was served as the gas zone and the bottom layer served as the bottom aquifer. The gas production was measured at different initial water saturations with and without wettability alteration from preferential water- to gas-wetness in gas zone. The experimental results showed that the water breakthrough time could be postponed and that the amount of water invaded into the gas zone could be reduced significantly by altering the wettability of the gas zone to gas wetness. The advantages of this approach to reducing water production were: 1) the permeability of the gas zone was not affected notably by the chemical treatment for wettability alteration; 2) the chemical treatment for wettability alteration had great longevity.
- Europe (1.00)
- Asia (0.94)
- North America > United States > Texas (0.69)
Abstract In gas condensate reservoirs, deliverability starts to decrease when retrograde condensation occurs. As the bottom-hole pressure drops below the dew-point, gas condensate and water build-up impede flow of gas to the wellbore. In order to stop the reduction in productivity, many publications suggest wettability alteration to gas-wetting as a permanent solution to the problem. Previous simulation work suggests an "optimum wetting state" to exist where maximum gas condensate well productivity is reached. This work has direct application in gas-condensate reservoirs, especially in identifying the most effective stimulation treatment which can be designed to provide the optimum wetting conditions in the near-wellbore region. In this work, we aim to show the existence of such an optimum state of wettability that result in maximum gas mobility and in an increase of the relative permeability curves. We present an experimental study on Berea sandstone rocks treated with a fluorinated polymer and investigate the optimum fluorinated polymer concentration that would alter the wettability to intermediate gas-wet. Different experimental techniquesincluding flow tests and spontaneous imbibition are conducted to examine the effect of treatments on wettability. Interaction between rocks and the fluids is studied using a MicroCT scanner. The studies in this area are important to improve the productivity of gas condensate reservoirs where liquid accumulates, decreasing production of the well. Efficiency in the extraction of natural gas is important for the economic and environmental considerations of the oil and gas industry. Wettability alteration is one of the newest stimulation methods proposed by researchers, and shows great potential for future field applications and further research studies.
- North America > United States > Texas (0.29)
- North America > United States > West Virginia (0.25)
- North America > United States > Pennsylvania (0.25)
- (2 more...)
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.96)
Abstract In the presented work the wettability conditions of reservoir chalk plugs have been characterised after water flooding with formation water, after spontaneous imbibition and water flooding by sea water, and after the first cycle of water alternating carbon dioxide flooding (CO2-WAG). Core plugs from a fractured chalk reservoir in the North Sea were used in the experiments carried out at reservoir conditions. Easily accessible sulphate in the core plugs was removed before the core plugs were drained to initial water saturation by using the porous disc method. Wettability acquisition was then carried out using stock tank oil. The wettability conditions of the chalk plugs were characterised by the spontaneous imbibition of water and the water-wet area determined by the sulphate wettability test. The water-wet area of reservoir chalk plugs water flooded by formation water was found to be rather small. The spontaneous imbibition of formation water was also rather low for companion core plugs. The prepared reservoir chalk plugs therefore appeared to be close to mixed-wet or preferential oil-wet. Sea water has earlier been found to improve the spontaneous imbibition of water into reservoir chalk plugs from the same field. After spontaneous imbibition and viscous flooding with sea water, the water-wet area of the core plugs was found to be on the average slightly larger than for the core plugs water flooded by the formation water. When the same core plugs were flooded with CO2, most of the oil was produced. After the following sea water injection, the water-wet area was found to be larger than before the simulated first cycle of the CO2-WAG flooding. During long term spontaneous imbibition experiments followed by viscous water flooding by sea water, slightly alteration of the wettability conditions towards more water-wet was observed. In the first cycle of a CO2-WAG process, the reservoir chalk plugs were found to become even more water-wet. Alteration of the wettability conditions to more water-wet during CO2-WAG processes can be important for the oil recovery in fractured chalk reservoirs, and should therefore be studied further.
- North America > United States > Texas (0.28)
- Europe > United Kingdom > North Sea (0.24)
- Europe > Norway > North Sea (0.24)
- (3 more...)
- Geology > Mineral (0.67)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.56)
- Geology > Geological Subdiscipline (0.47)
Improved Oil Recovery in Chalk: Wettability Alteration or Something Else?
Zahid, Adeel (Center for Energy Resources Engineering, Technical University of Denmark) | Stenby, Erling H. (Center for Energy Resources Engineering, Technical University of Denmark) | Shapiro, Alexander A. (Center for Energy Resources Engineering, Technical University of Denmark)
Abstract Improved oil recovery from low permeable chalk reservoirs is regarded as a great challenge because of their complexity and heterogeneity. Historically seawater salinity has not been considered as an important factor in determining the amount of oil recovered. Over the last decade, a number of studies have shown that waterflooding performance is dependent on the composition of injecting brine solution. Extensive laboratory research has been carried out in order to understand improved oil recovery from chalk using surfactant solutions and later on using the modified sea water. The researchers suggested wettability alteration towards more water wetting conditions to be the reason for improvement in oil recovery. In this paper, we are further investigating the reasons of observed improvement in oil recovery with sulphate ions. Is it really wettability alteration or something else also? Most of the previous work has been made on the basis of spontaneous imbibition using core plugs aged in crude oil. Our study is based on flooding and utilizes completely water wet cores without being aged in crude oil, just saturated with crude oil under vacuum. This would exclude alteration of wettability as a positive factor. Brine without sulphate is considered as the base injected fluid. Waterflooding experiments were carried out with brines without sulphate, as well as brines having different concentrations of sulphate. The effect of temperature, injection rate, crude oils and different sulphate concentration on the total oil recovery and the recovery rate was investigated. In Stevens Klint outcrop chalk samples, 10% increase in oil recovery was observed with sulphate enriched brine flooded core as compared to core flooded with brine without sulphate ions. We observed also 4-6 % increment of OOIP using brine with sulphate for water wet chalk at high temperatures. This clearly indicates improvement in oil recovery without wettability alteration, because chalk is already water wet. No increment in oil recovery was observed at 40 ºC and, neither, in experiments with North Sea crude oil. This clearly explained that crude oil type also plays a significant role in the effect that brine composition has on waterflood oil recovery. This study will help in getting more in depth understanding of seawater improved oil recovery process for chalk reservoirs.
- North America > United States (0.68)
- Europe > United Kingdom > North Sea (0.26)
- Europe > Norway > North Sea (0.26)
- (2 more...)