Organic geochemical studies and origin of black hydrocarbon material (heavy oil) produced from Risha gas field (Jordon): insights into produced contaminated organic-inorganic materials during production

Abstract

After several years of gas production, a black solid hydrocarbon material began to be produced along with the gas stream from the Risha gas field, in the northeastern part of Jordan. The main reason for the formation of this material is still unknown until this time, so knowing the source of this material is this study’s main goal. Organic geochemical studies for black solid material and effective source rocks (Lower Silurian shales) are used to determine the physical and organic components of the produced black solid material (heavy oil) and attempt to identify its source. The black solid material demonstrates high organic carbon (TOC = 12% by leco instrument) and a high calorific value, like those of oils, asphalts, and shale oils with moderate sulfur content. The gross composition of the black solid material sample is dominated by saturates and asphaltene but contains very low aromatic hydrocarbons reflecting the naphthenic oil type. Meanwhile, the Silurian extracts range between paraffinic and paraffinic-naphthenic organic matters. The biomarker indicators related depositional environment and carbon isotopic composition for the black solid material sample and Silurian extracts, show that they were relatively deposited in a reducing marine environment. The black material reveals lower maturity level than the Silurian extracts. Oil/source rock correlation study for the studied samples suggests strong affinity between the black material and Lower Silurian source rock in their source characteristics, suggesting that the black hydrocarbon material was expelled from the Silurian source rocks at low maturity stage as normal oil. This normal oil is subjected to secondary alteration process (evaporative fractionation) and was stored in the reservoir. It contaminated with some inorganic material that was introduced into the well as a component of a drilling mud additive or drill string lubricant or, potentially, in part, a corrosion product of wellbore tubulars, since significant iron was present in the sample.