Petrophysical Evaluation of Unconventional Najmah Formation of Kuwait - A Case Study

Abstract

Najmah Formation is an unconventional reservoir consisting of kerogen rich mudstone. It serves as an excellent source as well as reservoir and seal rock. It has low porosity and matrix permeability with sustained commercial production only in regions of high natural fracturing. Petrophysical evaluation of Najmah Formation poses many challenges and there is always a degree of uncertainty. The objective of this paper is to deliberate the methodology adopted in order to minimize the uncertainty. In the wells under study, a complete suite of logs were recorded including elemental log and nuclear magnetic resonance. Petrophysical evaluation was conducted using a mineral solver. Calcite, quartz, pyrite, illite, chlorite and kerogen were the minerals solved. The fluid volumes were obtained using Simandoux equation. Porosity was computed from sum of the fluid volumes, hence, intrinsically corrected for the presence of kerogen. TOC was computed based on the conversion of kerogen volume to TOC as proposed by Tissot and Welte (1978). The Langmuir isotherm methodology was used to determine the amount of adsorbed gas. The mineral volumes, porosity and TOC show good correlation with the core data. The computed adsorbed and total gas volumes confirm the economic potential of this unconventional reservoir. mineral dry weight fractions from neutron spectroscopy, compared with total gamma ray (red curve) and core clay dry weight fraction.