Transient Pressure Analysis of Horizontal Wells in a Multi- Boundary System

Horizontal wells can greatly increase the contact area of the wellbore and the pay zone; so they are commonly applied in oil reservoirs to enhance the production and ultimate recovery of oil and gas, especially, in low permeability formations. The purpose of this study is to develop a technique for the interpretation of transient pressure based on dimensionless pressure and pressure derivative. Type curve matching is one of the techniques that can be used to interpret the pressure data of horizontal wells in finite reservoirs. Starting from very short horizontal wells to extra-long wells, the pressure behavior of the wells has been analyzed for different conditions. The effect of the outer boundaries of the reservoir on the pressure behavior of the horizontal wells has been investigated for different configurations. Rectangular shape reservoirs with different dimensions have been used to study the pressure response in the well. Five flow regimes have been observed for regular length horizontal wells; early radial, early linear flow, pseudo radial flow, channel flow or late linear flow, and pseudo- steady state flow. Four flow regimes have been observed for the extra-long wells: linear flow, pseudo radial flow, channel flow, and pseudo-steady state or boundary-affected flow. Of course, those flow regimes do not always take place under all conditions. Pseudo-steady state flow is expected to occur after long production time. A pressure drawdown test was solved using the proposed type curve matching technique. The study has shown that the effect of the boundary on the pressure response of the horizontal wells and the type of flow regimes depend on the length of the horizontal wells and the distance to the nearest boundary. I. INTRODUCTION The use of horizontal wells for producing oil and gas from low-permeability and unconventional reservoirs is now very well established within the petroleum industry. The great increase of the surface area of the wellbore that allows fluids to freely flow from the reservoir to the wellbore is the main advantage of the horizontal well. Reducing the effects of the damaged zones and increasing the well deliverability are the direct impacts of this type of increment. Therefore, over the last two decades the number of horizontal wells that have been drilled worldwide has considerably increased due to the possibility of improving the well productivity and anticipating oil and gas recovery. Low-permeability and unconventional reservoirs are not the only common applications for horizontal wells. They also have been used successfully in fractured reservoirs: (a) to intersect natural fractures and effectively drain the reservoir; (b) in water and gas driven reservoirs to minimize water and gas coning; (c) in both low and high permeability gas reservoirs to reduce the number of producing wells; (d) in tertiary recovery application to enhance the contact between the well and the reservoir; and (e) finally, in offshore reservoirs, as well as in environmentally sensitive areas, to cut down the cost of drilling and the number of production facilities. Although, since the mid 1980s, horizontal well technology has provided the solutions for oil and gas production process where the conventional vertical technique either has failed or produced less than the desired rate, the rapid increase in the application of this technology during this period led to a sudden need for the development of analytical models that are capable of evaluating the performance of these horizontal wells. Giger, F. (1985) and Joshi, S. D. (1986) presented the applicability of horizontal wells in heterogeneous reservoirs and the impact of the well productivity using slanted or horizontal wells respectively. Spivak, D. (1988) explained that the advantages of horizontal wells, such as producvtivity increase, better sweep efficiency, and reduction of water and gas coning, have been reported by many researchers. At the same time, many researchers, such as Babu, D. K. and Odeh, A. S. (1989) and Goode, P. A. and kuchuk, F. J. (1991), have attempted to develop practical models to study the performance and productivity of horizontal wells.Over time, transient pressure analysis techniques have been favorably applied for the evaluation of horizontal well performance and reservoir characterization. Daviau et al (1988) presented solutions using the Newman product