Prospectus re Admission to the Official List - Heritage Oil

RPS EnergyHeritage Oil – Competent Persons ReportAs discussed above the Mishrif-Mauddud reservoir thickness varies considerably over the field. Themajority of this variation occurs in the Mishrif Formation. The thicker isopachs represent the platformcarbonates drilled at Henjam-1 and West Bukha-2 as opposed to the slope facies drilled at West Bukha-1and Khasab-1. These platform carbonates are cleaner better reservoir facies and therefore their extent hasbeen modelled when calculating GRV. Isochron maps have been used to determine the extent of this betterreservoir facies in line with previous studies carried out by Indago and Novus. Gross rock volumes werecalculated from the Top Mishrif to Top Nahr Umr for the whole field. The GRV of the better Mishrifreservoir was calculated from the top Mishrif to top Mishrif 1 unit over the area interpreted to be part ofthe platform above the fluid contact. The Mishrif 2 and 3 units GRV was then removed from the total fieldGRV so that separate reservoir parameters could be applied to both GRVs. These two separate cases werethen consolidated. For the Top Mishrif reservoir, a surface was calculated by isopaching 23 m down fromthe Top Ilam depth surface to account for the average thickness of the Ilam and Laffan units across thefield (16-27 m in the wells). The Top Mishrif 1 surface was calculated by isopaching 75 m up from RPS’sTop Mishrif surface to account for the Mishrif 2 and 3 units present in Henjam-1 (61m) andWest Bukha-2 (90m).The GRV for the Thamama Reservoir was calculated from Top Thamama to the fluid contact for all cases.RPS has independently reviewed the petrophysical data in West Bukha-1/1A and -2. Net to gross values inall cases were set to 100 per cent. as the pervasive fractures in the reservoir probably connected the fullvolume of matrix porosity. Clay volumes within the reservoir sequences are not high and there are fewindividual shaley beds, both the Thamama and the Mishrif-Mauddud are clean limestones with a few thinshale beds.Porosity in these tight carbonate reservoirs is very low. Average values for both reservoirs is between 1 and3 per cent. The Mishrif-Mauddud porosity was determined from petrophysics carried out on West Bukha-1and West Bukha-2A. The Mishrif-Mauddud was separated into two zones for volumetric purposes; theMishrif1-Mauddud unit and the Mishrif 2 and 3 units only being found in the northern part of the field.These units have slightly better reservoir parameters being clean platform carbonates as opposed to theslope facies found at West Bukha-1. The Thamama porosity was determined from petrophysics carried outon West Bukha-1 and West Bukha-2A.Water saturation is the most poorly constrained reservoir parameters. Low porosities make thedetermination of S w difficult and S w varies markedly between the West Bukha-1 and -2 wells. A wide rangeof S w has been used in the probabilistic calculation. A normal distribution of S w was used for bothreservoirs with a p90 value of 49 per cent. in both reservoirs and a p10 value of 18 per cent. in the Mishrifand 30 per cent. in the Thamama, respectively.FVF factors were recalculated by RPS and a range of values were applied in the volumetric evaluation.There is some uncertainty in the positions of the Gas Water Contact in the two reservoirs. Log evaluationis inconclusive and fluid contacts have been estimated from RFT data and production test results. Resultsfrom West Bukha-2 indicate that Mishrif-Mauddud reservoir is not connected to the Thamama reservoir.For the Mishrif-Mauddud a triangular distribution of possible contact depths was used to model theuncertainty. A minimum contact of 4,040 m TVDSS was taken from the deepest hydrocarbons tested inWest Bukha-2A, the most likely contact of 4,300 m TVDSS was based on RFT pressure data from wells inthe field and a maximum contact of 4,310 m TVDSS was based on the highest known water in thefield in the Khasab-1 test.For the Thamama a similar approach was used to model the uncertainty in water contact. Pressure data isinconclusive so a normal distribution based on a minimum contact of 4,163 m TVDSS, the lowest knownoil in West Bukha-2A, and a maximum contact of 4,268 m TVDSS from pressure data was used.86