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RI0226D. Production Optimization of Tide-Dominated Deltaic Reservoirs of the Lower Misoa Formation (Lower Eocene) LL-652 Area, Lagunillas Field, Lake Maracaibo, Venezuela, by W. A. Ambrose, E. R. Ferrer, S. P. Dutton, F. P. Wang, A. Padron, W. Carrasquel, J. S. Yeh, and Noel Tyler. 46 p., 29 figs., 1995. doi.org/10.23867/RI0226D.
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Structurally complex, heterogeneous, tide-dominated deltaic reservoirs in the Lower Misoa Formation (lower Eocene C members) in the LL-652 area of Lagunillas field in the Maracaibo Basin, Venezuela, have produced 166 million stock-tank barrels (MMSTB) of oil but have a low recovery efficiency of 22 percent. These reservoirs will contain more than 900 MMSTB of unrecovered mobile oil when primary recovery operations at the current 80-acre well spacing end. In this study we characterized lower Eocene reservoirs in the LL-652 area, Lake Maracaibo, to improve estimates of hydrocarbon reserves, to identify potential areas for secondary-recovery projects, and to establish a field-depletion plan to evaluate advanced recovery opportunities and extended development.
A significant remaining oil resource lies in poorly drained or undrained reservoir compartments confined by a combination of complex structure and depositional heterogeneity. Sealing and partly sealing faults, including northwest-trending normal faults and younger north-northeast-trending reverse faults, bound large-scale structural compartments. Stratigraphic heterogeneity is controlled by dip-elongate, distributary-channel, and tidal-ridge sandstones that commonly pinch out over distances of less than 2,000 ft (<610 m). Because these two facies compose most of the reservoir sandstones, they contain most of the remaining oil.
The main control on porosity and permeability distribution in the C members in the LL-652 area is depth. Volume of quartz cement in particular influences reservoir quality, and because volume of quartz cement increases significantly with depth, reservoir quality decreases with depth. Within each reservoir interval, however, depositional architecture controls porosity and permeability distribution. For example, significant permeability contrasts (as much as three orders of magnitude) exist locally between distributary-channel and tidal-flat, fluvial-estuarine channel and distal deltafront, and distributary-channel and delta-front facies, where clay clasts at the base of the distributarychannel facies may retard vertical fluid flow.
Cumulative production varies greatly in each reservoir interval as a result of differences in ages of producing wells, greater-than-average production in areas of repeat section and inferred increased fracture permeability in zones of reverse faults, and differences in net thickness of perforated intervals. The tide-dominated deltaic depositional fabric, however, controls net sandstone and net pay thickness of each reservoir interval and therefore must affect cumulative production.
We made maps of hydrocarbon pore volume (SoPhiH) and remaining oil on the basis of improved petrophysical characterization and production apportioning to specific reservoir horizons by permeability feet (kh). These maps indicate that most remaining oil lies in the poorly developed and structurally complicated north part of the field and where narrow (less than 2,000 ft [<610 m wide), high-SoPhiH belts are intersected by sealing and partly sealing reverse faults. The original oil-in-place resource base of the C members in the LL-652 area increased by 867 MMSTB (60 percent) to 2,318.2 MMSTB, mainly in the C-3-X and C-4-X members, by our identifying additional reservoir areas and improving quantification of porosity and other petrophysical parameters. Extended development on the current 80-acre (1,968-ft [600-m) well pattern that has 97 new wells will increase reserves from 127 to 302 MMSTB. However, 116 MMSTB, in addition to the 302 MMSTB, can be produced from 102 geologically based infill wells strategically targeted to tap areas of high remaining oil saturation in narrow sandstone bodies that pinch out over distances of less than the current well spacing. Horizontal and inclined wells in steeply dipping strata in the C-3-X and C-4-X members can capture additional volumes of poorly contacted mobile oil.
An integrated reservoir-characterization program that includes structural, stratigraphic, petrophysical, petrographic, production-engineering, and volumetric analyses can be used to improve oil-recovery operations in other mature, petroleum-producing provinces of Venezuela where many fields are nearing the first stages of primary depletion. The LL-652 area can serve as a model to demonstrate the most efficient means for recovering the remaining oil resource--a strategy targeting reservoir compartments defined by depositional-facies geometry and structure.
Keywords: Lagunillas field, Lake Maracaibo, lower Eocene, Lower Misoa Formation, reservoir characterization, resource-targeted reservoir development, tide-dominated deltaic reservoirs, Venezuela
Objective and Study Area
Data Base and Methods
Tide-Dominated Delta Model
Tidal Channel and Tidal Flat
Transgressive Sand Shoal and Shelf
Three-Dimensional Facies Architecture
Permeability Trends and Diagenetic Controls on Reservoir Quality
Diagenetic Controls on Reservoir Quality
Model for Calculating Shale Volume (VSh)
Porosity Model (Vsh-Porosity Transforms)
Permeability Model (Permeability-Porosity Transforms)
Cementation and Saturation Exponents
Fieldwide Formation Evaluation and Validation by Mapping
Sandstone Architecture and Recovery Optimization of Reservoir Intervals
Depositional Controls on Net Pay and SoPhiH
Upper C-4-X Submember
Sandstone-Body Geometry, Lithology, and Depositional Systems
Porosity and SoPhiH
Net Pay, OOIP, and Remaining Oil
Middle C-3-X Submember
Sandstone-Body Geometry, Lithology, and Depositional Systems
Porosity and SoPhiH
OOlP and Remaining Oil
Reservoir Development Opportunities and Strategies for Recovery Optimization and Reserve Growth
New Extended-Development Locations
Resource-Targeted lnfill Wells
Horizontal and Inclined Wells
1. Average recovery efficiency of oil reservoirs versus depositional systems
2. Location of the LL-652 area and Lagunillas field in the Maracaibo Basin and major Eocene stratigraphic sequences in the Maracaibo Basin
3. Type log, LL-652 area
4. Location of wells, type well, and cored wells, LL-652 area
5. Paleotectonic maps showing chronology of Tertiary tectonic episodes in the Maracaibo Basin
6. Present structural styles in the Maracaibo Basin
7. Fault-bounded compartments in lower Eocene strata, LL-652 area
8. Tide-dominated deltaic depositional model of lower Eocene reservoirs, LL-652 area
9. Core description of distributary-channel and related facies and net-sandstone map, middle part of the Middle C-5-X submember, LL-3075 well
10. Core description of distributary-channel facies truncating delta-front facies, Middle C-3-X submember, LL-3074 well
11. Core description of medial delta-front facies, ripple cross-stratified and laminated sandstones, and symmetrical ripples at the crest of the tidal sand ridge overlain by laminated siltstone, Middle C-5-X submember, LL-3075 well
12. Core description of distal delta-front facies, Lower C-3-X submember, overlying shelf and transgressive sand-shoal facies, Upper C-4-X submember, LL-3074 well
13. Core description of progradational tidal-flat facies and photograph of mud-draped flaser ripples in high-tidal-flat facies, Middle C-4-X submember, LL-2850 well
14. Core description of fluvial-estuarine-channel, upper estuarine-channel-fill, and transgressive sand-shoal facies, Lower C-6-X submember, LL-3080 well
15. Typical percent-sandstone patterns in offlapping, progradational sequences in the tide-dominated deltaic facies tract, C members, LL-652 area, showing superposition and basinward progradation of distal delta-front, proximal delta-front, distributary-channel and channel-mouth-bar, overlain by lower delta-plain facies
16. Average compositional classification of lower Eocene C-member sandstones by facies and by member, LL-652 area
17. Porosimeter-measured porosity as a function of present burial depth and quartz cement volume, of C-3-X through C-6-X sandstones, as well as plot of log permeability versus porosity
18. Comparison of petrophysical properties between core data and those calculated using porosity values derived from Vsh-porosity transforms, C-3-X member, LL-2850 well, and in the C-6-X member in the LL-3080 well
19. Comparison of water-saturation values calculated by Indonesian, Simandoux, and Waxman-Smit models and comparison of Vsh, porosity and permeability derived from gamma-ray and resistivity logs
20. Southwest-northeast stratigraphic dip cross section A-A' from cores, Upper C-4-X submember, showing permeability variation and basinward thickening of subunit nos. 1 through 4 in the transition from proximal to distal delta-front facies
21. Net sandstone, Upper C-4-X submember, LL-652 area
22. Maps of reservoir volumetrics, Upper C-4-X submember, LL-652 area, including arithmetic average porosity, SoPhiH, net pay, OOIP, remaining oil, and cumulative oil production
23. Net-sandstone-thickness map, Middle C-3-X submember
24. Southwest-northeast stratigraphic dip cross section B-B' and northwest-southeast stratigraphic strike cross section C-C', Middle C-3-X submember
25. Maps of reservoir volumetrics, Middle C-3-X submember, LL-652 area, including arithmetic average porosity, SoPhiH, net pay, OOIP, remaining oil, and cumulative oil production
26. Reservoir volumetrics, C members, LL-652 area
27. Field extensions in the Middle C-3-X submember
28. Map of remaining oil, Middle C-3-X submember, showing proposed new well locations, recompletions, redrilled wells, infill wells, and horizontal and inclined wells for the C-3-X and C-4-X members
29. Net-sandstone map, Upper C-4-X submember, east part of field, showing pilot waterflood area
Ambrose, W. A., Ferrer, E. R., Dutton, S. P., and others, 1995, Production Optimization of Tide-Dominated Deltaic Reservoirs of the Lower Misoa Formation (Lower Eocene) LL-652 Area, Lagunillas Field, Lake Maracaibo, Venezuela: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 226, 46 p. doi.org/10.23867/RI0226D.