The Wafra First Eocene Reservoir Partitioned Neutral Zone (PNZ), Saudi Arabia and Kuwait: Geology, Stratigraphy, and Static Modeling

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe First Eocene reservoir at Wafra Field was discovered in 1954 and has produced about 290 million barrels of 17-19° API, high sulfur oil.The dolomite reservoir is Eocene/Paleocene age. The average porosity is 35% and the average permeability is 250 md over the gross interval. Well log and core plug porosity values over 45% are common and measured permeability values range up to 5000 md. The First Eocene reservoir has an average depth of about 1300 feet and a gross thickness of about 750 feet. The OOIP is about 9 billion barrels.The reservoir largely consists of dolomitized packstones and grainstones deposited under arid to semi-arid conditions on a shallow, very gently dipping, low to moderate energy inner shelf or ramp setting in a gently dipping, restricted ramp environment. The presence of some interbedded evaporites suggests restriction was occasionally sufficient for the development of hyper-saline lagoons and sabkhas. The shallowing-upward cycles are capped by mud-dominated rocks, hardgrounds and exposure surfaces that are correlative with gamma ray highs that can be easily correlated across the 20 km length of the field and are the basis for the current sequence stratigraphic interpretation.Several full field and small, highly detailed reservoir models have been generated using stochastic workflows to assist management of on-going primary development as well as two steamflood test/pilot projects. The reservoir models utilize the new stratigraphic framework and are constrained by over 285 wells with high quality porosity logs and six wells with high quality core descriptions and core plug data. Model properties were distributed by stratigraphic layer and constrained by layer-appropriate data (or transforms) and layer-appropriate semivariograms. The range parameter for the semivariograms models used in full field static models varied between 1100-2200 m with moderate anisotropy in the direction N120°E. Conversion Factors1 foot = 0.3048 meters 1 meter = 3.2808 feet 1 mile = 1.6093 km

Probabilistic Forecasting and Model Validation for the First-Eocene Large-Scale Pilot Steamflood, Partitioned Zone, Saudi Arabia and Kuwait

“…The reservoir properties by stratigraphic interval for the LSP area of the 1E ranged as follows: unit thickness-7 to 57 ft; average porosity-24 to 43%; average water saturation (S w )-27 to 59%; and permeability 20 to 960 md (Meddaugh et al 2007). Table 1 provides a summary of the semivariogrammodel parameters used to build the LSP area static model.…”

“…The layer-specific correlation coefficients varied from À0.5 to À0.8. Additional details regarding the workflow and its application to this reservoir are provided by Meddaugh et al (2005a) and Meddaugh et al (2007). The use of petrophysically derived lithofacies as an additional constraint was investigated but not ultimately used because of a relatively low correlation between predicted and actual lithofacies in the validation wells.…”

“…1). Discovered in 1953, it is the shallowest of five significant producing reservoirs at Wafra and contains world-class volumes of heavy oil-more than 10 bbl of 13 to 19 API oil (Meddaugh et al 2007). A simplified stratigraphic column for the PZ is shown in Fig.…”