Source rock characteristics of organic-rich shales in the Late Jurassic Lam Member and their contribution to oil and gas generation potentials in Al-Jawf exploration region, NW Yemen

Abstract

The shale intervals in the Late Jurassic (Tithonian) Lam Member were collected from four exploration wells in the Al-Jawf region, northwestern Yemen, for combination of organic geochemical and microscopic investigations. This study mainly attempts to provide information on source rock characterization, including quantity, quality, and thermal maturity, and evaluate their suitability as petroleum generation potential, thereby contributing for future petroleum exploration along the Al-Jawf region. The geochemical findings reveal that the shale intervals in the Lam Member have favorable hydrocarbon source rocks with total organic carbon (TOC) contents between 0.50 and 6.43 wt. %, and they have laterally changed from one well site to another. The shale samples also have hydrogen index (HI) values between 50 and 433 mg HC/g TOC, resulting in two dominant organic facies of types II-III and III kerogen, with little type II, and thereby contributing to generate both oil and gas. The high contributions of mixed types of II-III and III kerogen were also demonstrated from the presence of the marine sapropelic organic matter and vitrinite derived from terrigenous plant input as observed by visual kerogen examination. According to both maturity indicators of geochemical T max (417-451 °C) and vitrinite reflectance (VRo) values (0.36-0.86%), the Lam shale intervals from the examined wells in the Al-Jawf region are currently in immature to peak mature of oil window. These thermal maturity levels of the organic matter intervals in the analyzed Lam shales are affected by the burial temperature distributions with the depth. In this regard, the source rock characteristics of the analyzed Lam shale samples in the studied wells are further distributed on the maps, and show that the Lam shales in the southwestern part of the Al-Jawf exploration region in the area around Kamaran-01 well are considered to be effective source rocks for generating amounts of oil.