Reconciling Log-Derived Water-Saturation and Saturation-Height Function Results

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 175053, “Reconciling Log-Derived-Water-Saturation and Saturation- Height-Function Results Through Resistivity Modeling, Core-Log Integration, and Image-Log Data: A Case Study From Deepwater Gulf of Mexico,” by Javier Miranda, Michael Rabinovich, Jeffry Hamman, and Maryam Mousavi, SPE, BP, prepared for the 2015 SPE Annual Technical Conference and Exhibition, Houston, 28–30 September. The paper has not been peer reviewed. Saturation-height functions (SHFs) play a key role in reservoir description and in quantifying oil in place. The functions must compare well with other sources of water saturation (Sw), such as core measurements and well-log interpretations, when they are available. The authors have reconciled different Sw sources through a reliable SHF function based on the Brooks-Corey model with parameters optimized for the Gulf of Mexico (GOM) Thunder Horse (TH) Field. The function is used to populate oil volumes in the 3D static and dynamic models. General Description of the Hydrocarbon Field TH is located in a six-block “lease unit” of the Mississippi Canyon (MC) area of the deepwater GOM. The field is approximately 69 miles from the Louisiana coastline in water depths ranging from 6,000 to 6,500 ft. The TH facility consists of a taut-wire-moored semisubmersible system with production, drilling, and quarters (PDQ). The PDQ is located near the southern boundary of MC 778. The PDQ is designed to handle 250,000 BOPD, 200 MMscf/D, and 140,000 B/D of produced water. The facility was also designed to handle 300,000 B/D of mixed seawater/produced water for injection. The TH wells are located in subsea drill centers, with additional satellite subsea-production wells located where the reservoir structure dictates. Sixteen producers have been brought on line since first oil on 14 June 2008. The total volume produced as of the end of 2014 is estimated at 300 million BOE. Oil and water rates (December 2014) are 100,000 BOPD and 26.500 BWPD, respectively. The TH discovery contains hydrocarbon resources in two structural closures commonly referred to as the TH South (THS) and TH North (THN). TH Reservoir Distribution and Architecture. The current depositional model for TH is that all three reservoir intervals are part of a stacked sequence of Miocene lower slope aprons. In a general architectural model for a single slope apron, the proximal region is dominated by amalgamated channels, bypass lags (acting as baffles and barriers), and lateral complexity. Net/gross ratio (NTG) can vary significantly in the proximal region, depending on the distance to sediment sources. The medial portion of the apron is dominated by more-sheet-like sands interspersed with the occasional silt- or mud-rich unit, and the distal portion of the apron is dominated by interlayered sand, silt, and mud units. In a vertical sequence, the apron model leads to an increase in system energy and channelization from bottom to top. After the apron healed the terrain, sediments began bypassing down the slope and were able to erode into the apron itself. This led to the formation of canyons and canyon-fill successions that segmented the original reservoirs and yielded isolated compartments and major production barriers.