Evaluation of the performance of horizontal wells is an important aspect in the enhancement of their productivity. This study provides mathematical computations, and analysis for theoretical well and reservoir considerations. The study investigates how well design and reservoirs geometry affect the overall performance of a horizontal well in a completely bounded reservoir throughout its productive life. A horizontal well in a rectangular reservoir with completely sealed boundaries is considered and the effect of dimensionless well length L D \hspace{.25em}{L}_{\text{D}} , dimensionless reservoir length x eD \hspace{.25em}{x}_{\text{eD}} , and dimensionless reservoir width y eD {y}_{\text{eD}} on the pressure response over a given period of production using dimensionless time t D {t}_{\text{D}} is studied. The mathematical model used was derived using source and Green’s functions presented in part I of this study. Appropriate well and reservoir parameters are considered and the respective dimensionless parameters are computed which are then used in computing dimensionless pressure P D {P}_{\text{D}} and its dimensionless pressure derivative P D ′ \hspace{.25em}{P}_{\text{D}}^{^{\prime} } . From the computations, the results obtained are analysed in diagnostic log–log plots with a discussion of the flow periods. The results obtained indicate that an increase in dimensionless well length decreases pressure response during the infinite-acting flow at early times and during transition flows at middle time but increases the pressure response during the pseudosteady state flow at late times. The dimensionless reservoir width and length are observed not to influence dimensionless pressure response during the infinite-acting flow at early times and during the transition flows at middle time, only affecting the prevalence time of the flow periods. However it is observed that during the pseudosteady state flow at late times, dimensionless pressure response reduces with increased dimensionless reservoir length and width.
When horizontal wells are compared with verticals wells, their production is always higher. If their performance can be improved, they can even be more productive. Considering a horizontal well in a completely bounded oil reservoir, when the well has been producing for some time and the effect of the boundaries is evident on the flow, the pressure distribution can be approximated by considering the effects of the boundaries on the flow. Considering when a pseudosteady state flow is attained this study presents a mathematical model for approximating pressure distribution for late time for a horizontal well in an oil reservoir with sealed boundaries. We use appropriate Source and Green’s functions to develop the model. The model developed show that when the flow reaches all the boundaries a pseudosteady state flow is attained and thus pressure distribution is influenced by the oil reservoir geometry especially its width and length. Considering that the thickness of the oil reservoir will be small compared to the length of the well, the oil reservoir width and length will determine the pressure response. This will influence the flow period occurring. By considering all aspects of the flow, the model can be applied to approximate the pressure distribution for as long as the well can continue producing.
Horizontal wells are more productive compared to vertical wells if their performance is optimized. For a completely bounded oil reservoir, immediately the well is put into production, the boundaries of the oil reservoir have no effect on the flow. The pressure distribution thus can be approximated with this into consideration. When the flow reaches either the vertical or the horizontal boundaries of the reservoir, the effect of the boundaries can be factored into the pressure distribution approximation. In this paper we consider the above cases and present a detailed mathematical model that can be used for short time approximation of the pressure distribution for a horizontal well with sealed boundaries. The models are developed using appropriate Green’s and source functions. In all the models developed the effect of the oil reservoir boundaries as well as the oil reservoir parameters determine the flow period experienced. In particular, the effective permeability relative to horizontal anisotropic permeability, the width and length of the reservoir influence the pressure response. The models developed can be used to approximate and analyze the pressure distribution for horizontal wells during a short time of production. The models presented show that the dimensionless pressure distribution is affected by the oil reservoir geometry and the respective directional permeabilities.
To enhance the productivity of horizontal wells, it is of necessity to ensure that they perform optimally. This requires an understanding of how the reservoir’s geometry, anisotropy and well design affect the pressure response. Mathematical formulations can be used to simulate pressure response in the wellbore and the data obtained can be analysed to obtain well and reservoir parameters that can aid performance and evaluation. In this study, a mathematical model that can be used to approximate pressure response in a horizontal well is formulated, and a detailed mathematical analysis that can be used to obtain well and reservoir parameters are provided. A horizontal well inside a rectangular drainage volume with sealed boundaries is considered and the effect of each boundary on pressure throughout its productive life is studied. In the analysis, investigations on how the reservoir parameters can be approximated over a given period of production are conducted. This is achieved by identification of the appropriate source and Green’s functions. These source functions allow us to formulate a mathematical model for dimensionless pressure. Considering the diagnostic plots for both dimensionless pressure and dimensionless pressure derivative, mathematical analysis studies the possible behaviour of the plots. Analysis indicates that the reservoir anisotropy can be approximated during the infinite-acting flow at early times when other parameters are known. Further, when the first boundary is felt, in this case the vertical boundary, the horizontal permeability can be approximated during the transition flow periods at middle times. Finally, at late times when all the boundaries have been felt and a pseudosteady state flow is evident, reservoir dimensions can be approximated. These results can significantly improve well test analysis and enhance the performance evaluation of a horizontal well.
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