Mangala is currently the largest discovered oil field in the Barmer Basin of Rajasthan, India, with a STOIIP of over 1 billion barrels contained in the stacked clastic fluvial reservoirs of the Fatehgarh Group. The field was discovered in January 2004 and a fast-track appraisal program followed, involving the drilling of eight more wells and a host of data acquisition activities in 2004-2007. Production startup under waterflood is planned for 2009, with an initial plateau production rate of ~100,000 bopd. As there is no analog Fatehgarh production anywhere else in the country, multi-well and single-well interference tests provided essential large-scale areal and vertical reservoir connectivity data that helped to ground the geologic and reservoir models that were the basis of the field development plan.
Areal interference tests were conducted by recording a baseline MDT pressure trace throughout the entire reservoir section in the observation wells. After production/injection began in the source well, additional MDTs were conducted in the observation wells to monitor pressure changes throughout the reservoir section, thus providing both an areal and a vertical measurement as to how the pressure response spread. An important test was carried out by producing Mangala-1 and monitoring pressure responses in three adjacent wells that were 300 - 1,500m distant. This test demonstrated excellent areal communication and a fair degree of vertical communication through the reservoir.
A second key areal interference test was carried out in conjunction with a water injectivity test in Mangala-2 while observing the pressure response in Mangala-1 and Mangala-4. Although a response was observed in Mangala-1 at a distance of 2,700m, no response was observed 700m away in Mangala-4, confirming that the shale correlated between Mangala-2 and Mangala-4 is a barrier to fluid flow. Finally, a single-well vertical interference test was carried out in Mangala-5; this demonstrated that a typical shale layer that occurred between the producing and observation zones in the well was actually of limited areal extent, and provided a "match point" for the geologic model.
This paper explains the design, operations and results interpreted from each test and how these results were key factors in geological modeling of the field and planning the initial development concept.