Reservoir Simulation Improves Implementation of Midway Sunset Steamflood

Abstract

SPE Members Abstract Thermal reservoir simulation was utilized to understand, make development recommendations, and project the performance of the Monarch C steamflood in a portion of Mobil's South Midway Sunset field. The Monarch, a thick sequence of complex turbidite deposition, is characterized by extreme geological heterogeneity (lithofacies-controlled permeability and saturation variation, and mudstone barrier layers). Steamflood performance in the Monarch is related directly to the reservoir quality, and the path of steam flow is significantly influenced by the numerous laterally extensive mudstone barriers. The fine grain clay-bearing sediments were deposited on the anticline, distal from the source, whereas the coarser grain sediments, with little clay, were deposited on the more proximal syncline and steep dip areas. Consequently, steamflood performance improves relative to the crest since reservoir quality improves (including oil saturation), clay content decreases, and structure (dip) becomes more pronounced. The simulation models were constructed to capture the heterogeneity. Two models were constructed, a single pattern model for a pattern with good performance, and a multi-pattern strip model that linked patterns of good performance with poorly performing patterns on the crest of the structure. Simulation results indicated the initial completion strategy, that ignored the mudstone barriers, often resulted in misalignment between injector and producer completions that severely limited performance. A complete overhaul of the well completions was required to improve the steamflood. Subsequent to the simulation work, the steamflood was re-engineered, based on intensive pattern-by-pattern and well-by-well reviews, to include producer recompletions and limited entry steam injectors. Steamflood performance improved following the redesign. Introduction Mobil's MOCO 35 Fee Property in the South Midway Sunset field is located in Kern County, California. The Monarch, composed of four retrograding turbidite reservoir complexes (A, B1, B2, and C), offers an unusually complex geological environment for steamflood development. These sands were produced under primary and cyclic steam until an aggressive steamflood development plan was initiated in the mid-1980's for three of the reservoir complexes. A four-pattern pilot was started in 1986-87 (five-acre nine spots) and followed by further expansion in 1989-90. Steamflooding often includes a significant gravity drainage contribution, and therefore performance can be enhanced in reservoirs that have significant structure. In general structural terms, the Monarch sands consist of an anticline (present during deposition) that gently slopes into a syncline. Past the syncline, the sands have been greatly uplifted through Post-depositional folding resulting in a highly dipped structure ("steep dip"). The 12-pattern 1989 Expansion lies primarily on the top of the anticline, with the southern 3 patterns in the synclinal region. Figure 1 shows MOCO Section 34 and 35, the structural configuration, and the location of the pilot and the 1989 Expansion area. Subsequent development has moved west of the anticline, but has concentrated on the synclinal region and the highly productive steep dip area to the south and southwest. Figure 2 shows a schematic strike cross section for the three main sands of the Monarch: B1, B2, and C. Figure 3 shows a dip cross section for the same sands. P. 279

Cyclic-Steam Injection Initiation Project in Heavy Oil Reservoir – A Simulation Study

“…The geology of the Monarch Sands (1,2,3) consists of thin units (2 to 10 ft.) aggregating about 1,000 ft. in stratigraphic thickness. The beds dip 60 to 70 degrees and the trap is provided by a truncating unconformity with 20 degrees dip (Fig.…”