TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNumerous waterflooding projects are under way throughout the world for increased recovery. Water injection tests of oil zones are frequently undertaken during the planning phase of waterfloods. Analysis of the bottomhole pressure data recorded during these tests not only provides similar information to that obtained from production tests concerning the well and the reservoir characteristics but also allows the mobility ratio between the injected and resident fluids to be determined.Conventionally, pressure fall-off test data is analyzed using semilog plot of bottomhole pressure versus time. This paper is the extension of the Tiab's Direct Synthesis Technique 10-15 to pressure injection and Fall-off tests in water injection wells.Direct synthesis is a transient pressure analysis technique [10][11][12][13][14][15] , which uses log-log plot of pressure and pressure derivative vs. time. Thus, different straight line portions indicating different flow regions are directly analyzed. Direct synthesis is very useful in conditions of short and early time pressure data missing tests. It also verifies the results since it uses more than one equation for the estimation of reservoir parameters such as permeability, wellbore storage coefficient, and skin factor.Finally, field examples of pressure falloff analysis are presented to illustrate use the direct synthesis and results are compared with those from type curves and conventional semilog analysis.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIn highly heterogeneous reservoirs classical characterization methods often fail to detect the location and orientation of the fractures. Recent applications of Artificial Intelligence to the area of reservoir characterization have made this challenge a possible practice. Such practices consist of seeking the complex relationship between the fracture index and some geological and geomechanical drivers (Facies, porosity, permeability, bed thickness, proximity to faults, slopes and curvatures of the structure) in order to obtain a fracture intensity map using Fuzzy Logic and Neural Network.This paper shows the successful application of Artificial Intelligence tools such as Artificial Neural Network and Fuzzy Logic to characterize naturally fractured reservoirs. A 2D fracture intensity map and fracture network map in a large block from Hassi Messaoud field have been developed using Artificial Neural Network and Fuzzy Logic.This was achieved by first building the geological model of the permeability, porosity and shale volume using stochastic conditional simulation. Then by applying some geomechanical concepts first and second structure directional derivatives, distance to the nearest fault, and bed thickness were calculated throughout the entire area of interest. Two methods were then used to select the appropriate fracture intensity index. In first method well performance was used as a fracture index. In the second method, which consists of a new proposed approach, a Fuzzy Inference System (FIS) was built. With such system static to dynamic data was coupled to reduce the uncertainty and resulted in a more reliable Fracture Index. The different geological and geomechanical drivers were ranked with the corresponding fracture index for both methods using a Fuzzy Ranking algorithm. Only much important data were selected to be mapped with the appropriate fracture index using a feed forward Back Propagation Neural Network (BPNN). The neural network was then used to obtain a fracture intensity maps throughout the entire area of interest. A mathematical model based on "the weighting method" was then applied to obtain fracture network maps, which resulted in a deep insight about the major fracture trends.The obtained maps were compared in the end and the results show that the proposed approach is a feasible methodology to map the fracture network.
This paper presents an analysis method of the transient pressure behavior of dual lateral wells. Conventionally lateral wells have been analyzed using horizontal well analysis techniques. As we will show in this paper, that if the phase angle between the two lateral sections differ from p, they can not be treated as horizontal well and such practices any result erroneous reservoir properties. An infinite conductivity solution for dual lateral wells was developed by coupling both; the infinite conductivity horizontal well model and the superposition concepts. From the sensitivity analysis study, it was found that infinite conductivity solution for dual lateral wells is affected by the horizontal anisotropy, phasing of the lateral sections, dimensionless horizontal separation, mechanical skin, wellbore storage. It is less affected by the dimensionless vertical separation and the contrast between the dimensionless lateral lengths. Transient pressure behavior of dual lateral wells appears to be more pronounced in the cases:for a phase angle decreasing,for a horizontal separation decreasing, andfor a horizontal anisotropy increasing. The effect of the phase angle decreases while increasing the dimensionless lateral lengths and horizontal separation. The effect of the horizontal anisotropy on the pressure behavior is more pronounced for high phase angles. The wellbore storage dominated flow period tends to be more affected for small dimensionless lateral lengths, LD. The effect of unequal lateral lengths and vertical separation are pronounced only at early times. The intermediate time pseudoradial flow period displayed by dual lateral wells is more distinguishable from the wellbore responses in the cases of a large phase angle and a high value of the horizontal separation. It is worthwhile to note that the responses of dual lateral wells having a phase angle, ß=p, may be viewed as an equivalent single horizontal well. Also Tiab's Direct Synthesis (TDS) technique methodolgy for dual lateral wells has been developed, which adds to the analysis of such wells. Few examples are solved in a step-by-step manner, which demonstrate the use of the method developed. Introduction The productivity improvement expected from horizontal wells is usually proportional to the length of the well. As the length of the horizontal well increases, drilling and well control become extremely difficult. In addition, transportation of a large volume of fluid along a long horizontal borehole results in considerable wellbore pressure losses affecting the productivity. In term of the well coverage, dual lateral wells are expected to provide an excellent alternative to the long horizontal wells. A thorough treatment of the well itself based on accurate computational methods for analyzing and predicting the well performance is needed for better understanding the dual lateral pressure behavior. Practically, the main characteristic features of the responses is that the dual lateral wells may be viewed and analyzed as an equivalent single horizontal well. However, this approach is a great simplification and is suitable only for certain phase angles and anisotropy ratios. Therefore, this approximation is restricted to a specific reservoir-well configuration and its use may introduce significant error in estimating reservoir parameters. For this purpose, we present a semi analytical dual lateral model based on that of the horizontal wells. According to our knowledge, there does not exist such a model to date. Literature review Over the last decade, a considerable amount of work has been published on various aspects of multilateral wells. Most of these works have been presented on the performance of multilateral wells as means of new technology to improve productivity. But only few of them treat the transient pressure behavior of multilateral wells. Karakas, Yokohama and Arima(1) have presented an interpretation of several transient tests conducted in multilateral wells. Using a numerical solution, they indicated that most multiple drain hole systems can be approximated by an equivalent single layer, single drain hole systems.
This paper investigates the effect of higher concentrations (0–100%) of CO2, H2S, and N2 on natural gas well deliverability, reserve estimation, and pressure test analysis quantitatively. Physical properties of natural gases such as viscosity and compressibility are corrected according to the concentrations of the contaminant gases such as CO2, N2, and H2S present in it. These contaminant gases have profound impact on pressure test analysis. The Carr et al1 viscosity correction chart allows adjusting the viscosity up to 15% concentration of these contaminant gases. However, Wichert and Aziz2 compressibility correction chart allows up to 80% concentration of the CO2 and H2S. Tiab3 developed an analytical method to estimate pseudopressure function for 0–100% combined-concentration of CO2, H2S, and N2. His pseudopressure was first re-plotted to simplify the procedure and then it was used to analyze the deliverability, pressure tests, and decline curves quantitatively. The analysis was performed with Carr et al1 viscosity correction chart, pure CO2 properties, and then with Tiab's corrected pseudopressure. Pure CO2 properties were used due to the fact that the sample data has 98.256% CO2. During this study it was observed that the compressibility factor has a little effect on analysis since it is a volume-related property. Viscosity, however, has the largest effect on the analysis since pressure is transmitted through the fluid in the porous media and viscosity works against it. It was also observed that the numerical method of calculating pseudopressure function introduced successive error in the analysis. Number of pressure data points also contributed to theerrorinnumericalintegrationofthepseudo-pressure function. Analysis of field as well as simulated examples resulted an absolute error range of 13–75% in the permeability estimation in pressure tests, 77% in deliverability tests, and 20–95% with pressure derivative. Error in AOF was observed as 15% and as high as 32 % in reserve estimation. Introduction The High energy (Temperature and Pressure) environment and the presence of Oxygen rich compound turned many of the hydrocarbon reservoirs into CO2 rich reservoirs. Such reservoirs usually are of low commercial value due to higher concentration of sour gases. Fig.1 shows the existence of CO2 rich reservoirs in United States. Texas, New Mexico, Colorado, Mississippi, Wyoming, and Utah are the states with abundance of this natural resource. Two major consumers of CO2 are the Chemical and Petroleum industries. Due to its miscibility in both water and oil, CO2 has found its niche in EOR operations of miscible flooding. However, the potential for CO2 flooding and its other application will be significant if it is found in enough quantity. Thus, its use and production as a natural resource requires the development of engineering techniques to analyze such reservoirs effectively.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractDownhole oil-water separation (DOWS) provides the ability to conduct a cross-waterflood using a single wellbore that penetrates stacked waterflood zones. In this application of DOWS technology, production from one waterflooded zone is used as the inlet stream to the separation process. The oil-rich stream is produced to the surface while the water stream is injected into the second zone as shown in Fig.5.Potential benefits include reduced well count, reduced lifting costs, reduced expenditures for surface water handling facilities, reduced treating costs, smaller surface footprint and reduced environmental risk. Potential disadvantages include DOWS installation costs, more expensive workovers, more difficult and costly monitoring and larger wellbore requirements.DOWS technology is widely viewed as a potentially highly valuable technology with a high price tag and a high risk of failure. A major failure node for DOWS installation is the injection zone. Injection into a water flooded zone reduces the injectivity problems, and provides a benefit from the work required to inject the water stream. If a DOWS installation can economically be justified on its own merits anywhere, it will be in a cross-water flood application. The question remains; Can a DOWS crosswater flood be economically justified?This paper is divided in four parts. First, DOWS technology in general and cross-waterflood application in particular are briefly described. Second, the operational advantages and disadvantages of this application of DOWS technology are briefly discussed. Thirdly the parameters of economic model are reviewed in some detail. Lastly, the characteristics of a waterflood operation that can benefit economically from this technology are summarized.
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