Comprehensive Evaluation of Horizontal Wells with Transverse Hydraulic Fractures in the Upper Bahariyia Reservoirs

Abstract

The objective of this work was to investigate the viability of converting existing conventional vertical wells into horizontal wells with multiple transverse fractures in the Upper Bahariyia reservoirs of the Western Desert of Egypt. These reservoirs can be characterized as two thin, low permeability layers with no crossflow between them. The productivity of these reservoirs was very limited when producing by conventional vertical wells. Reservoir simulation was used to evaluate various combinations of transverse fractures in horizontal wells producing. These results were compared with simulation results for conventional vertical wells, with and without vertical fractures. Only infinite conductivity fractures were considered. Early transient behavior as well as pseudosteady-state behavior were simulated. The results show that horizontal wells with transverse fractures appear to make production of the Upper Bahariyia reservoirs economically feasible. It has been shown that the productivity index of horizontal wells with transverse fractures is mainly affected by the distance between the outermost fractures and not by the number of fractures nor the spacing between them. Between fractures perforations has been shown to have negligible effects on increasing the productivity of horizontal wells with transverse fractures in these reservoirs. Introduction Problem Description of Upper Bahariyia Reservoirs. In the Western Desert of Egypt, there exists a laminated shaly sand formation named the Baharivia formation. The Upper set of the Bahariyia formation (designated as Upper Bahariyia reservoirs) had significant hydrocarbon and oil reserves compared to the total Western Desert estimated reserves. Despite the high concentration of reserves in these reservoirs, it was difficult to produce them economically due to the lamination, relatively low permeability and thin layers. Also some of these reservoirs had high bubble point pressures (near its original reservoir pressure) which forced the wells to be produced below the bubble point pressure. This caused an additional reduction in oil rates due to reduction in the oil relative permeability caused by gas evolving and accumulating near the wellbore The Upper Bahariyia reservoir mainly consist of two thin layers (6 and 3ft), with permeability ranging in each layer from 2 to 10 md. In a large number of these reservoirs the bubble point pressure is around 200 to 300 psi below the original reservoir pressure. Attempts have been made on several wells to test and produce the Upper Bahariyia reservoirs in different areas of the Western Desert. Most of these tests showed negative results. A typical behavior of these wells is to initially produce with oil rates ranging from 200 to 600 bopd, then the production rates quickly decline and the well eventually dies within a few months. This typical performance is true even when lifting pumps are used. Also recent unsuccessful attempts included fracturing the vertical well producers and implementing secondary recovery methods as water flooding. Horizontal Wells With Transverse Fractures. Today horizontal drilling is a reliable and proven technique, providing operators of hydrocarbon reservoirs with a new tool for efficiently producing oil and gas reservoirs. Hydraulic fracturing can improve the performance of horizontal wells dramatically, especially in reservoirs with low transmissibility. It is now known that hydraulic fractures increases the candidate reservoirs for horizontal well applications. Figs. 1 and 2 presents the candidate reservoirs for both horizontal wells and horizontal wells with multiple hydraulic fractures. P. 47^

Optimal Design of Nonuniform Multiple Transverse Fractures for Horizontal Wells in Tight Gas Reservoirs

“…The expression for estimating β is developed by Cooke (1973): 6 30.88 10 ' = ' b a β × (14) The coefficient b' and exponent a' is determined by the mesh size illustrating in Table 1. The following iteration procedure (shown in Fig.4) is generated to take into consideration the non-Darcy effect on production behavior.…”

“…Economidies et al (1991) developed a numerical simulator to simulate diverse aspects associated with horizontal wells intercepted by verticals fractures of infinite-and finite-fractures. Elrafie and Wattenbarger (1997) investigated the viability of converting existing conventional vertical wells to horizontal wells with multiple transverse fractures in targeted reservoirs and evaluated various combinations of infinite conductivity transverse fractures in horizontal wells. The result of their work shows that the productivity index of horizontal wells with transverse fractures is mainly affected by the distance between the outmost fractures, and not by the number of fractures or the spacing between them.…”

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The state-of-the-art in natural gas production

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Production Forecasting of Hydraulically Fractured Conventional Low-Permeability and Unconventional Reservoirs Linking the More Detailed Fracture and Reservoir Parameters

“…Huffman et al (1996) and Elrafie and Wattenbarger (1997) present fracture length and net present value (NPV) optimization for infinite conductivity fractures. Richardson (2000) presents fracture length and NPV optimization by fixing the F CD at a value of 30.…”