Impact of Sandstone Reservoir Heterogeneity on Well and Reservoir Management and Development Strategies in Northern Oman

Abstract

A portfolio of oil fields was reviewed over the last years to identify common issues and classify/quantify further development opportunities. The reservoir is a spatially and vertically heterogeneous group of sandstones. Common development approaches and issues are directly related to depositional environment: - A high net-to-gross reservoir unit consisting of deltaic and glacial outwash deposits has historically received the most attention due to generally good aquifer support. Remaining infill drilling opportunities are related to attic oil pockets and/or lower shoreface units that were by-passed by the aquifer or not targeted previously. A revised completion strategy allows completion of high and low perm units in different zones. - A low net-to-gross and lower permeability unit dominated by heterolithic and fine-grained deltaic and tidal flat deposits is planed to be developed by hydraulic fracturing. Some fields show this unit to have a conventional reservoir component, consisting of fluvial/estuarine channel complexes. These channel complexes are a more attractive development in itself, allow acceleration and could also improve the economics of the remaining tighter parts. Another unit consists of stacked fluvial channel complexes interbedded with overbank/floodplain deposits typically developed by depletion drive. Highly variable net-to-gross is translated into variable aquifer support even within the subunits in individual fields. Water flooding will be trialed in units/fields with insufficient aquifer support. Fines migrating from the overbank/floodplain complexes into the sandstones are thought to be responsible for common lower than expected productivity. Low productivity due to clay minerals is mitigated by a dedicated perforation strategy. The locally better than expected permeability of overbank complexes is expected to facilitate cusping of gas in few fields. General insights gained from the portfolio review and knowledge transfer between the fields was used to identify additional WRM opportunities and consolidate the overall hydrocarbon maturation strategy while detailed insights were used to initiate selective model updates and allow quantification/ranking of opportunities.

AAPG Datapages/Search and Discovery Article #90328 © 2018 AAPG Middle East Region GTW, Maximizing Asset Value: Integrating Geoscience with Reservoir Management & Facilities Optimization, Muscat, Oman, April 30 – May 1, 2018