Abstract
Evaluating a reservoir to looking for hydrocarbon bearing zones, by determining the petrophysical properties in two wells of the Yamama Formation in Siba field using Schlumberger Techlog software. Three porosity logs were used to identify lithology using MN and MID cross plots. Shale volume were calculated using gamma ray log in well Sb-6ST1 and corrected gamma ray in well Sb-5B. Sonic log was used to calculate porosity in bad hole intervals while from density log at in-gauge intervals. Moreover, water saturation was computed from the modified Simandoux equation and compared to the Archie equation. Finally, Permeability was estimated using a flow zone indicator. The results show that the Yamama Formation is found to be mainly limestone that confirmed by cuttings description and this lithology intermixed with some dolomite, in addition to gas and secondary porosity effects. Generally, the formation is considered clean due to the low shale volume in both wells with the elimination of the uranium effect in well Sb-5B. The calculated porosity was validated by core porosity in YC and YD units. Modified Simandoux gives a better estimation than the Archie equation since it takes into account the conductive of matrix in addition to the fluid conductivity. Five equations were obtained from porosity permeability relationship of core data based on five hydraulic flow units reorganized from the cross plot of reservoir quality index against normalized porosity index. The overall interpretation showed that YC and YD units are the best quality hydrocarbon units in the Yamama Formation, while YA came in the second importance and has properties better than YB. Moreover, YE and YFG are poor units due to high water saturation.
Highlights
The evaluation of the petrophysical properties is considered an essential part when describing the features of the hydrocarbon reservoirs where the interaction, as well as the characterization in the reservoirs and non-reservoir rocks between the rock and fluids, helps to determine various properties such as porosity which represents the network character of the pores, in addition to permeability and saturation that describes the path of the fluid and its distribution in the network, respectively (Cannon, 2016)
Mineral identification (MN ) and matrix identification (MID) cross plots were used in this study and they are determined from the following equations (Dewan, 1978) : M= ((∆tf- ∆tlog) /) * 0.01 (1)
A good insight of lithology was obtained by using MN and MID cross plots, these plots show the lithology of Yamama consists mainly of limestone which is supported by cutting description in addition to some dolomite with secondary porosity indication and gas effect
Summary
The evaluation of the petrophysical properties is considered an essential part when describing the features of the hydrocarbon reservoirs where the interaction, as well as the characterization in the reservoirs and non-reservoir rocks between the rock and fluids, helps to determine various properties such as porosity which represents the network character of the pores, in addition to permeability and saturation that describes the path of the fluid and its distribution in the network, respectively (Cannon, 2016). Many types of well logs can be used to calculate porosity as indirect method which requires the use of various factors that represent a property of the formation and the fluid within(Jenkins, 1960).One of the fundamental task is the calculation of water saturation which has the impact on fluid distribution in the reservoir so as a result the calculations of hydrocarbon in place and due to the degree of uncertainty that combined with several measurement required, it become more difficult to compute rather than porosity (Cannon, 2016). Hydraulic flow unit used to split the reservoir into zones and each flow unit can be identified by applying a flow zone indicator (FZI) which used to calculate permeability where the core data is not available (Amaefule et al, 1993)
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