Success Story of a Waterflood Project in a Geologically Complex, High Viscosity Oil Reservoir in a Major Brownfield in South Oman

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA major reservoir in a large brown field in South Oman has been on production for more than 25 years. The reservoir comprises glacial sandstones of Palaeozoic age and is highly heterogeneous with wide variation in reservoir characteristics at scales smaller than well spacing. These variations include impermeable diamictite and shale beds and multi-Darcy gravel or conglomerate beds. The reservoir geology is further complicated due to the presence of faults and fractures that often provide highly conductive vertical pathways to the aquifer. The reservoir crude has high viscosity (90 cp) and moderate to low API gravity (22 deg API oil). The field has been developed using vertical and horizontal wells in different phases of development. Water-flooding is in operation in the reservoir for more than 6 years. Injectors comprise vertical injectors in five spot pattern, horizontal injectors and inclined aquifer injectors in the flanks. Different water injection philosophy for different areas of the field has been adopted considering factors like primary drive mechanism operative in the reservoir, presence or absence of vertical barriers to flow, pre-existing field development pattern and more importantly future development for maximizing recovery from the reservoir over the entire life cycle. Despite the geological complexity of the field and adverse mobility ratio conditions under which water-flooding is being carried out, the reservoir has responded very favourably to water flooding. The production decline trend from the reservoir has been arrested and reservoir pressure has increased in most areas of the field after initiation of water injection. The paper presents the success story of water-flooding in a geologically complex reservoir containing high viscosity oil. The paper clearly illustrates that the success of a water-flood in a complex reservoir rests on implementation of a tailormade development plan with flexibility to make changes to the same based on data from reservoir surveillance. The importance of well and reservoir management to maximize the value of waterflood is clearly brought out.

Enhancing Value of Polymer Flood Project with Proactive Well and Reservoir Management

“…The reservoir production history is shown in Fig.2. Development of the reservoir has been carried out in different phases and consists of an initial phase of vertical well drilling, EOR pilot schemes, horizontal in-fills with limited water injection and full-field water injection (Choudhuri et al, 2008). Polymer flooding in the reservoir commenced in early 2010.…”