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The Main Sultanat of Oman Gas Field is comprised of two deep tight gas clastic reservoirs, separated by thick shale layer, and has been on production since 1999. These reservoirs are encountered at depth ranges of 14,000 - 17,000 ft and the top reservoir is a rich gas condensate followed by a lean gas for the lower reservoir. Permeability is in the range of 0.01 to 10 mD, porosities of 1 % to 14% and this field being a swing producer, actual production is in the range of 700 - 1,000 MMsfcd. To ensure achieving a maximum value, from such complex reservoirs, the field has gone through several development stages. The first stage has focused mainly on appraisal and development wells to obtain better understanding of well and reservoir performance and further data acquisition for better reservoir characterisation. The second stage of the Field Development Plan (FDP), in 2005, was an update of the FDP reflecting all the information that have become available since the commission of the field as well as the production performance gained from the previous 5 years of production. Further optimization of total number of wells, better prediction of the field performance and firming up the first stage of depletion compression were the key elements of the FDP update. Hence, first stage depletion compression plant was pursued and commissioned in 2010. In addition, velocity strings from 51/2" to 27/8", for maximum utilisation of low producing wells, were evaluated and more appraisals activities, for further scope maturation, were assigned. The third stage of the FDP update has been completed. The key objectives were to validate the previous FDP, in particular, wells and reservoir performance as a result of stage-1 depletion compression. Besides, phase-2 depletion compression was proposed and the remaining development drilling were re-evaluated, optimised and confirmed. Furthermore, a plan to mature contingency reserves, from poor reservoir intervals, was initiated and associated studies, such as geomechanical models and fracturing optimisation were performed. In this paper, a case study of developing a complex and tight deep gas reservoir will be discussed. The experience of applying phase approach and associated value will be shared and how the multidisciplinary team came up with the best Field Development Plan taking into consideration the different challenges and options taken by every discipline to put the best development strategy to get the optimum ultimate recovery from the field.

Future exploitation strategies sensibilities were based on accelerated natural depletion or different schemes for pressure maintenance by gas injection. Since there were not PVT's analysis available for the gas condensate region of the S3M/SG-44 reservoir, a flash was estimated for the equilibrium liquid composition in order to reproduce the gas zone properties. Daily oil production rates were input data for the COMPSIM production rates were input data for the COMPSIM simulator, and daily gas production, GOR and reservoir pressure were history latched. Sensibility studies were similar to those conducted for the M3U/MVR-52 reservoir. GEOLOGICAL DESCRIPTION Reservoir M3U/MVR-52 in the MATA-R/Zapatos field and S3M/SG-44 in the Mapiri field are located, as shown in Figure 1, in the Greater Oficina Area of the eastern Venezuela sedimentary basin. Geologically, they fore part of a regionally identified monocline, with a smooth dip to the north. The M3U sand, MVR-52 reservoir belongs to the lower section of the Oficina formation. In the fluvial deltaic depositional environment of the area, sand bars are present towards the north, and distributary channels towards the south-east. The sand shows good development towards the eastern part of the reservoir, thinning in the center, and good development, with poor sand quality toward the western pert of the reservoir. The reservoir is bounded to the south by a normal east to west striking fault, lateral pinchouts to the east and to the west, and by a pinchouts to the east and to the west, and by a water-gas condensate contact to the north, Fig.2 Abstract The effects of gas injection into two gas condensate reservoirs in eastern Venezuela were analyzed in order to establish optimum exploitation schemes. One of the reservoirs, the M3U sand, MVR-52, in the Zapatos field, is actually subjected to a pressure maintenance process. The other reservoir, the S3M sand, process. The other reservoir, the S3M sand, SG-44, in the Mapiri field, is a dual gas condensate, black oil reservoir, currently at a primary depletion stage. primary depletion stage. Sensibility studies were made for both accelerated natural depletion and pressure maintenance through the injection of lean gas. These simulation studies were made utilizing a phase behavior simulator and a compositional phase behavior simulator and a compositional simulator (COMPSIM). The first was used to calculate equilibrium constants at different pressure. In order to achieve this, it was pressure. In order to achieve this, it was necessary to characterize the fluids in function of six (6) pseudocomponents, which represent the mixture of the pure components as given by PVT analysis. COMPSIM is a three-dimensional, three-phase, compositional simulator, which allows to compute pressure and saturation distributions, as well pressure and saturation distributions, as well as the distribution of the fluid components in the oil gas-condensate phases. Mass exchange of each component between oil and gas phases is ruled by the equilibrium constants under conditions of thermodynamic equilibrium. In the case of the M3U/MVR-52, after introducing pseudocomponents for the characterization of pseudocomponents for the characterization of initial fluid compositions, the dew point pressure, liquids deposition and relative pressure, liquids deposition and relative vol-es were latched using the compositional phase simulator. Production and pressure history phase simulator. Production and pressure history matching were attained through the COMPSIM.

The Geology of Production Study of The Northern of Monagas Oil Fields was done with the participation of a multidisciplinary team of Geologist,Geophisicists, Petrophisical and Reservoir Engineers. Being the main objective to elaborate the best geological model for the known reservoirs in the area by means of new geological. seismical and engineering techniques. All this was valuable to cuantitY reserves as well as to optimize the explotaition schemes proposed for the medium and long term planning.

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