Petrophysical evaluation and fluid substitution modeling for reservoir depiction of Jurassic Datta Formation in the Chanda oil field, Khyber Pakhtunkhwa, northwest Pakistan

• Main Authors: Natasha Khan, Khaista Rehman
• Format: Article
• Language: English
• Published: SpringerOpen 2018-07-01
• Series: Journal of Petroleum Exploration and Production Technology
• Subjects: Kohat Basin; Datta Formation; Sands; Chanda oil field; Petrophysics; Gassmann fluid substitution
• Online Access: http://link.springer.com/article/10.1007/s13202-018-0513-9

Abstract Petrophysics coupled with rock physics studies are significant in the evaluation of well and field potential, and to construct subsurface models based on rock properties. This case study combines petrophysics and fluid substitution modeling for reservoir characterization of the producing Datta Formation in the Chanda oil field of Kohat Basin. The Datta Formation interval of two wells, Chanda-1, and Chanda Deep-1, is analyzed to calculate petrophysical parameters including gross thickness, net thickness, net to gross ratio (NGR), porosity (PHA), permeability (K), and water saturation (S W). The Datta Formation represents fair to good porosity in the range of 7–13%. Water saturation shows low values lying in the range of 31–36%. The formation is interpreted from gamma ray (GR) log trends, where sand packages dominantly represent a left box-car and irregular trend. Cross-plots, such as density porosity (RHOB-NPHI), gamma ray-density (GR-RHOB), gamma ray-porosity (GR-NPHI), and thorium–potassium (Th–K), were used for lithological identification in the studied wells, and indicated arkosic and micaceous sandstone as the dominant lithology with shale. Evaluation of petrophysical parameters shows that the Datta sands have high hydrocarbon saturation in the area. The fluid substitution modeling was applied to clastics of the Datta Formation for field development. One hydrocarbon-bearing zone (zone 1) was identified in Chanda-1, while four hydrocarbon-bearing zones (zones 1, 2, 3, and 4) were identified in Chanda Deep-1. Fluid substitution results at the Datta level showed that the P-wave velocity and density varied when the hydrocarbon phase was substituted completely with water. With the substitution of brine with oil, there was a change in compressional wave velocity (V p) and a decrease in density (RHOB), while the shear wave velocity (V s) was stable and unaffected by the change of fluid density and saturation. The results of this research could be used to predict saturation types of reservoir using seismic data and to identify pay-zones, and map reservoir saturation to drill for oil and gas.