Prediction of thermal maturity by indirect methods using seismic attributes in the central part of the Persian Gulf

AbstractIn this paper, a method is proposed for the prediction of thermal maturity in the source rock using indirect methods. The applied data are well logs (neutron, density, resistance, and acoustic) in 13 wells and seismic data in six oil and gas fields in the central part of the Persian Gulf. Well-logs and seismic data are much more abundant than geochemical data and cover an extensive area in the oil and gas fields. These properties compensate for the lack of geochemical data that are scattered and limited to a few wells. This study is carried out in two steps. First, the amount of thermal maturity in the Kazhdumi Formation is calculated from well logs and is presented as an index in each well. Data obtained from organic thermal evaluation analyses are used to validate the results of thermal maturity prediction. These data include Rock-Eval pyrolysis in two wells. Then, seismic data are processed and studied in two-dimensional sections at the location of the target fields. In this step, seismic attributes are extracted from the seismic data using the multi-attribute regression analysis method, and thermal maturity is calculated using these attributes. Prediction is performed by probabilistic neural network analysis, and a seismic section is extracted indicating variations in thermal maturity in the Kazhdumi Formation.Keywords: Source rock, Thermal maturity, Well log, Seismic attribute Introduction The Kazhdumi Formation is an important source rock in the Persian Gulf basin, in the south of Iran (Bordenave Burwood, 1990). Thermal maturity of the Kazhdumi Formation is low in the central Persian Gulf compared to the eastern and western sectors (Rabbani 2008; Ghasemi-Nejad et al. 2009; Rezaie Kavanrudi et al. 2015; Rabbani et al. 2014; Baniasad et al. 2019). This formation is over-mature in proximity to the Hormoz Strait. The TOC content of this formation depends on the variety of depositional environments across the basin, increasing to the northwest with a maximum of 6 wt% in the proximity of the Hormoz strait (Rezaie Kavanrudi et al. 2015; Noori et al. 2016). The kerogen type is mainly ⅡS and type Ⅲ in different areas (Ghasemi-Nejad et al. 2009). The stratigraphic equivalents of the Kazhdumi Formation are the Burgan Formation in the west and south of the Persian Gulf (Kuwait), producing hydrocarbons from the second-largest hydrocarbon oilfield in the world, and the Nahr-Umr Formation in Qatar and Iraq. The Burgan and Nahr-Umr formations consist of flu