Integrated field and well reviews followed by logical activities are being taken to address the voidage and declining pressure in Yibal. This is to ensure that target daily oil rates are achieved, and UR is maximized, in the largest oil producing asset in Oman, which delivers almost 15% of the total country production from a heavily faulted and fractured carbonate anticlinal structure, on stream since 1969. Water injection initiated in 1972 has gone through a series of stages; vertical oil phase injectors for lateral sweep, vertical aquifer injection for vertical sweep and later some horizontal deep aquifer injectors. The injection serves the dual purpose of pressure management and produced water disposal. The field has suffered negative voidage for quite some time, leading to rapid reservoir pressure depletion. Past studies have identified uneven vertical and lateral sweep due to uneven subsurface water distribution as a result of the complicated fracture and fault patterns as well as the subsurface hydro-dynamics and flow mechanisms. This has left the remaining oil in pockets that are becoming more difficult to produce. The high field average BSW has led to a situation where oil wells are closed in for surface facilities constraint and, or subsurface water injection capacity. Further, the uncertain water movement into producing wellbores makes production optimization activities risky. Recently, quite a number of injectors have been taken offline for integrity repairs and are only gradually coming back on stream after extensive and often expensive repairs. The implementation of a voidage replacement program which includes understanding the reservoir dynamics, identification of the worst hit low pressure areas, and prioritization of the short, medium and long term remedial activities is on going. Increased focus on gross offtake management, injection well stimulation, water shut off in producers, conversion of poor producers to injectors, and drilling of new injectors is showing returns in flattening of the decline rate of oil production. The issues around water injection as well as oil producer integrity are gradually being addressed. Several learning points for the implementation of the proper reservoir and voidage management have also been captured. The importance of human resources both in terms of numbers, level of experience and skills set, has also been recognized and the optimum balance of these is being worked on. Introduction The Yibal field (Fig 1), discovered in 1963 and brought on stream in 1969, currently produces oil (from the Shuaiba reservoir) and gas (from the Natih reservoir). Both streams are managed by different Asset teams.

An exploratory appraisal campaign of the greater Musallim Oil Field area was executed in 2003. The main objective was to test the Shuaiba pancake reservoir and to confirm the presence of reservoir on the flanks, prove calibration of the porosity trends derived from acoustic impedance data, provide structural control and determine oil saturations below crestal oil-down-to (ODT) of 1443 mtvdss. The appraisal campaign was designed to test the ODT pancake model concept in Musallim. The pancake concept is a model where 2–12m thick good reservoir zone overlies poor quality reservoir. Based mainly on oil saturations logged from vertical wells, this boundary was previously interpreted as an oil water contact. However saturation changes represent an ODT as a function of reservoir quality, and permeability in particular. Prior to this campaign, two existing flank wells, (Musallim Deep-1H1 and Tibr-1H1) targeted deeper reservoirs as their primary objective but found oil saturations up to 50% below the ODT of 1443 mtvdss, then defined as the OWC in the 2002 Musallim field FDP. The 2003 appraisal campaign by PDO's Near Field Exploration team has proved the viability of the pancake model and significantly increased the reserves of the Musallim Field. It has extended the life of the field and opened up many new development possibilities. Another outcome of the exploratory appraisal campaign was that the eastern flank of the structure came in shallower and was confirmed by Tibr-2 which targeted deeper objectives that resulted in a re-assessment of the velocity model used in depth conversion. Success of the Musallim Rim campaign together with Tibr-2 well shows that these oil rims associated with the Shuaiba pancakes and flank plays are attractive targets. Introduction: The Musallim Field is situated in Central Oman some 40km NNW of Saih Rawl Field and 60 km SE of the Al Huwaisah Field (Fig. 1). The field was discovered in 1971 by Musallim-1 and was appraised by Musallim-2.The field is a low relief anticlinal structure and the hydrocarbons are trapped in the Shuaiba Formation limestone andsealed by overlying Albian Nahr Umr shales. The reservoir fluid consists of 280 API and 4.8 cp oil. It has a GOR of 21 m3/m3 and is undersaturated by some 10167 Kpa compared to the initial reservoir pressure of 17082 kPa. Fig. 1 Regional map of the Arabian Peninsula Regional Setting The area of interest is located in Central Oman sector of PDO's Block-6 concession. The Musallim Field lies between two major oil fields, (Saih Rawl and Al Huwaisah), which are producing from the platform carbonates of the Shuaiba Formation. The Shuaiba in this part of the concession shows a thickness (75 - 82 m). The Musallim field is developed as an elongated NW-SE trending low relief anticline. Stratigraphy The Shuaiba Formation occurs throughout Oman, except where eroded by the base Nahr Umr unconformity in South Oman (Fig. 2). The persistence of the slightly deeper argillaceous facies through the upper part of the Shuaiba in the Lekhwair area reflects a northwards transition into the Bab Member of the Upper Shuaiba described in Abu Dhabi.