This paper presents a new approach to forecast the behaviour of an acid-fractured well by numerical simulation. Unlike the known conventional methods, the present technique applies the "Dual-Porosity System" theory.Several wells were indiVidually successfully using their production history the pre-fracture and post-fracture pressure tests in a single continuous run.The forecasted pressures and oil rates were in good agreement with their actual values.Also,the fracture lengths imposed to match the post-frac history showed good agreement with the values derived from test analyses. This method ,thus, provides a viable predictive tool and a means to support the well test interpretation results by respecting more precisely, as we believe, the flow pattern in the Vicinity of the wellbore and within the fractured medium.
The Dulang Unit Area covers the central part of the highly heterogeneous Dulang Field which is located offshore Peninsular Malaysia. The Unit Area consists of 19 stacked shaly sandstone reservoirs which are divided into about 90 fluid blocks containing multiple fluid contacts. The estimated Original-Oil-In-Place (OOIP) is in the vicinity of 700 mIllion stock tank barrels (MMSTB). Production commenced in March 1991 and is currently maintained at more than 50,000 barrels of oil per day (BOPD). Reservoir simulation is one of the vital tools which has been employed from the very beginning to develop as well as manage this Dulang field. This paper documents a case history dealing with the construction of numerical models of two distinct fault blocks in one of the major reservoirs (E14). The simulation studies led to the consolidation of the development plan as well as reservoir management strategies. They also greatly aided in improving the reservoir characterization. Introduction The Dulang field is a major oil field in the Malay Basin. It is located about 130 km offshore east coast of Peninsular Malaysia in water depths of about 76 m in the South China sea (Figure 1). Following field discovery in 1981, an additional 13 exploration/appraisal wells were drilled confirming an oil and gas column of up to 150 m in 19 stacked sandstones (classified into Groups D and E) of Middle-Late Miocene age (Figure 2). The Dulang field is an anticline which is approximately 24 km long and 3.5 km wide. It is owned jointly by Petronas Carigali Sdn. Bhd. ("Carigali") and Esso Production Malaysia Inc. ("EPMI"). The western and eastern portions are operated separately by Carigali and EPMI, respectively. Carigali, in addition, operates the central area which was unitized in 1988 and is referred to as the Dulang Unit Area (Figure 3). Both Carigali and EPMI are contractors to Petronas, the National Oil Company of Malaysia and operate under production sharing contracts (PSC's). The OOIP is in the order 700 MMSTB. The field came on stream in March 1991 and is at present producing in excess of 50,000 BOPD. The crude gravity averages about 39 API. The associated gas production is about 45 million standard cubic feet per day and it contains more than 50% CO2. A total of 90 wells will have been completed from three 32-slots platforms by the end of the present drilling campaign expected to be wound up in April 1995. These will translate into 163 oil production strings, 8 gas injection strings and 26 water injection strings. The discovery of Dulang field was based on the interpretation of 2-D seismic data. In 1984, a 3-D survey was acquired and interpreted. The greater resoluton of the 3-D data revealed substantially different fault patterns.
The Dulang Field is located offshore east coast of Peninsular Malaysia in water depths of approximately 75 m. The field, discovered in 1981, is about 24 km by 3.5 km. After drilling 14 exploration/appraisal wells by both Carigali and its partner Esso Production Malaysia Inc., the central part of the field was developed as a unitized area in November 1990. Three 32-slot platforms have been installed in the unitized area, and development drilling is ongoing. Production commenced in March 1991 and is currently maintained at approximately 50,000 BOPD. The estimated OIIP (oil-initially-in-place) for the unitized area is in the order of 700 million barrels. There are 19 reservoir sands in Groups D and E which are of Middle-Late Miocene age. During the exploration/appraisal phase, oil and gas were encountered in the Group E and only gas in the Lower D1 reservoirs. Wireline formation pressure test data taken in the Lower D 1 reservoir in these wells plotted along a common trend with a gradient of 0.06 psi/ft. The lowermost gas pressure point was only 6 m above the normal hydrostatic gradient. It was therefore concluded that an oil column, even if present, would be thin. At the time, it was understandable that the gas pressures plotted along the same trend because the hydrocarbon column of the Lower D1 reservoir was large and extended beyond the limits of the major faults, suggesting a common pool. However, during the development drilling phase, it was discovered that the Lower D1 sandstone was a major oil reservoir, with estimated oil-in-place of about 100 million barrels. Oil columns of 75 m and 40 m have been proven up in the northern and southern flanks of the field, respectively, in the Lower D1. In addition, development plans were flexible enough to be able to effectively exploit the discovery. The well and formation pressure test data suggest that the Lower D 1 has a common pressure system in the gas cap over the central part of the field but different systems in the oil columns. Faulting is suspected to have provided both conduit and seal at different times to accommodate this phenomenon. P. 385
The Dulang field, discovered in 1981, is a major oil field located offshore Malaysia in the Malay Basin. The Dulang Unit Area constitutes the central part of this exceedingly heterogeneous field. The Unit Area consists of 19 stacked shaly sandstone reservoirs which are divided into about 90 compartments with multiple fluid contacts owing to severe faulting. Current estimates put the Original-Oil-In-Place (OOIP) in the neighbourhood of 700 million stock tank barrels (MMSTB). Production commenced in March 1991 and the current production is more than 50,000 barrels of oil per day (BOPD). In addition to other more conventional means, reservoir simulation has been employed from the very start as a vital component of the overall strategy to develop and manage this challenging field. More than 10 modelling studies have been completed by Petronas Carigali Sdn. Bhd. (Carigali) at various times during the short life of this field thus far. To add to that, Esso Production Malaysia Inc. (EPMI) has simultaneously conducted a number of independent studies. These studies have dealt with undersaturated compartments as well as those with small and large gas caps. They have paved the way for improved reservoir characterization, optimum development planting and prudent production practices. This paper discusses the modelling approaches and highlights the crucial role these studies have played on an ongoing basis in the development and management of the complexly - faulted, multi-reservoir Dulang Unit Area. Introduction The Dulang field is one of the most significant offshore oil fields in the Malay Basin which is also home to several other major fields such as Seligi, Tapis, Guntong etc. Dulang field is located about 130 km off the east coast of Peninsular Malaysia in water depths of about 76 m. in the South China Sea (Figure 1). Following field discovery in 1981, an additional 13 exploration / appraisal wells were drilled confirming an oil and gas column of up to 130 m in 19 stacked sandstones (classified into Groups D and E) of Middle - Late Miocene age (Figure 2). The Dulang field is an anticline which is approximately 24 km long and 3.3 km wide. The western and eastern portions are operated separately by Carigali and EPMI, respectively. Carigali, in addition, operates the central area which was unitized in 1988 and is referred to as the Dulang Unit Area (Figure 3). Both Carigali and EPMI are contractors to Petronas, the National Oil Company of Malaysia and operate under production sharing contracts (PSC's). The OOIP is in the order of 700 MMSTB. The field came on stream in March 1991 and is at present producing in excess of 30,000 BOPD. Cumulative oil produced amounted to about 60 MMSTB at the end of 1994. The crude gravity averages about 390 API. A summary of the range of reservoir and fluid properties is shown on Table 1. The associated gas production is about 43 million standard cubic feet per day and it contains more than 30% CO2. P. 161
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