Even though the over all performanceof the project is consideredto be good, more informationis needed A study was made to determinethe burned volume regarding the reservoir properties and firefront and the location of the firefront in the Miga P2,3
An analytical model is presented which describes the pressure behaviour of a well completed in a reservoir wherein natural fractures occur over a limited area around the wellbore. The flow in the reservoir is treated as a composite reservoir flow problem, the region adjacent to the wellbore being considered as a fractured medium and the outer region as an homogeneous one. Wellbore storage and skin effects are included in the solution, and the flow in the fractured region is mathematically described by Warren and Root's double porosity theory. Dimensionless log-log plots of pressure vs time show the existence of several well-defined flow regimes, which can be used in the interpretation of pressure transient tests data to estimate the fractured region parameters as well as its radius around the well. This last parameter is of considerable importance for the purposes of reservoir development or infill drilling programs, for it would allow the reservoir engineer to estimate the areal extension of the fractures in the reservoir. Based on the model results for different values of the parameters involved, guidelines are provided for conducting and interpreting a pressure test with the objective of determining the characteristics and areal extent of a natural fracture system. Introduction Due to the large hydrocarbon reserves held by naturally fractured reservoirs, their explotation has become a challenging task for the petroleum industry. Estimation of fracture parameters such as fracture volume, directional trends, storage capacity, etc. are of vital importance for the proper design of explotation strategies. In the past 25 years, a considerable theoretical effort has been made to describe the behaviour of these reservoirs. Based on the work done by Barenblatt, Warren and Root proposed an analytical solution which has been used successfully to describe the transient pressure behaviour of a naturally fractured reservoir. Crawford et al presented field data with no wellbore storage, Sup porting the validity of the Warren and Root model. Mavor compared the Warren and Root's solution with other models and concluded that, from an engineering standpoint, it was the most practical. Also, he extended their work to account for wellbore storage and skin effects. Recently, Da Prat, et al. and Benson and Lai have applied the Warren and Root model to the interpretation of field data with apparent success, indicating the model's practical usefulness. In essence, Warren and Root idealized the fractured reservoir as two distinct systems: matrix and fractures (see Fig. 1). The flow towards a fully penetrating well is assumed to occur only through the fractures. Both the cases of an infinite and a closed reservoir have been treated extensively by the authors mentioned and others. However, to the authors' knowledge, the case of a well completed in a reservoir where natural fractures occur only over a limited area has not been modeled. Such a reservoir situation may be idealized as a composite reservoir model (see Fig. 2) where the inner region adjacent to the well is considered as a radial naturally fractured zone that behaves as proposed by Warren and Root, and an outer radial homogeneous reservoir of either infinite or finite extension. Composite reservoir problems have been the subject of considerable attention in the petroleum literature over the last 25 years. In general, the composite model consists of a well completed in the center of a circular inner region with fluid and rock properties different from those in an outer region. P. 35^
The prediction of coning behaviour is critical to assessing the development potential of thin oil rims and to forecasting performance during the thinning phase of oil rims in general, towards the end of field life. Although coning behaviour has been investigated extensively for homogeneous reservoirs, relatively little has been reported on coning in fractured reservoirs.
For a naturally fractured reservoir the existence of two semi-log straight lines when analysing real pressure transient data is seldom observed and some existing models for interpretation of fractured systems have always been subjected to controversy. In this study an analysis of pressure transient data taken in wells completed in fractured reservoirs in Western Venezuela has shown the existence of two well-defined parallel semilog straight lines which confirms the Warren and Root model from a practical viewpoint. The data was analysed using the typecurve corresponding to the solutions for a well with wellbore storage and skin in a reservoir with double porosity (pseudo-steady state flow). The analysis provides values for the dimensionless fractured storage parameter, w and the dimensionless matrixfracture permeability ratio, A which are considered to be representative of a two-porosity system. Finally, a production forecast analysis is made for the reservoir using the obtained values of w and A·
Horizontal drilling has been used successfully to increase productivity of wells in several regions of the world. In Venezuela the first horizontal well was drilled by Lagoven, S.A. subsidiary of Petroleums of Venezuela (P.D.V.S.A.)in 1989 in the lake Maracaibo area. This paper presents this well test design and interpretation. The test consisted of a drawdown followed by a buildup with simultaneous measurements of pressure and sandface flow rates. The acquired downhole flow rates eliminate the need for the assumption of constant wellbore storage and allow a morerigorous analysis. The formation transient response was analyzed to identify the reservoir flowpatterns and its parameters. The techniques used included pressure derivative, convolution, convolution type curves and convolution derivative. The difficulties encountered while performing the test and actions taken to solve them are also discussed. The existing geological and core-analysis data provided the additional information required to decide which reservoir model to use, and allowed a more conclusive interpretation of the test results.
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