Interpretation of seismic data utilizing DMB depositional model lead to a significant South Louisiana discovery

Abstract

Without an understanding of the DMB depositional In an area of close grid, good quality seismic model, it is almost impossible to properly interpret data, an earlier interpretation without the the seismic data representing such sequences. As a depositional concept resulted in several deep dry result, these areas are erroneously mapped and many holes. Remapping the same data with the help of the unnecessary dry holes are drilled. In this paper are depositional model resulted in a trend play of nine presented the results of a study in an area DMB propsects with an acreage position of more than with classic Miocene DMB sequences where all seismic 25,000 acres. The first of these DMB prospects (DMB data was mapped utilizing the DMB depositional model. 7) was drilled in August of 1992. The well logged The results were phenomenal several new prospects three gas sands, one oil sand, and three other sands were mapped old dry holes were properly explained which could potentially be productive. The lowermost and new discoveries were drilled. of these sands, which is in the process of being hooked up now, tested 1.6 MMCF/day with 60 bbls. of Distributary mouth bars (DMB's) are the most condensate at 6/64th choke from perforations at 13705prolific deltaic sandstone reservoirs. DMB's build 13710.5 with a flowing tubing pressure of 9500 psig at the mouth of distributary channels areas of and a shut-in tubing pressure of 9541 psig. extremely dynamic sedimentation. Rapid deposition of large quantities of sands at this site over a This significant discovery is the first of a platform of highly unstable, water-logged, plastic trend of nine DMB prospects and is a direct result of prodelta shales triggers a sequence of geologic the application of the DMB depositional concept in the events which juxtapose good quality DMB sands between mapping of the log and seismic data. good source and seal rocks (marine and prodelta shales) on contemporaneously developed trapping structures (rollover anticlines downthrown to the growth fault). The order of events (which are for the most part penecontemporaneous) in the DMB sequence development are as follows: (1) Deposition of DMB sands over prodelta shales. ( 2 ) I n i t i a t i o n and growth of a CD fault on the updip side of the DMB depopod. (3) Tilting of beds on the downthrown side of the fault and development of a rollover anticline producing the critical north dip. (The crest of the rollover anticline generally coincides with the middle part of the DMB.) (4) Extensive diapirism of prodelta shales around the sand depopod (an adjustment to the imbalance caused by sediment loading) generating upthrown shale ridges behind the fault, north of the DMB depopod, and frontal shale ridges basinward of the DMB sands. Often the shales upheave in the core of the rollover anticline; as such, the sands on the crest of the rollover become thin. (5) Geopressuring of sediments as the fault seals the migration path of waters and (6) finally, in its abandonment stage, capping of the whole system with thick transgressive marine shales, a very attractive package for oil and gas generation and trapping.