Preservation of crude oil with different properties and implication for deep oil exploration

An evaluation of deep crude oil preservation ability identifies the depth limit of crude oil exploration. Thermal simulation products of crude oils with different properties and limestone media were analyzed and combined with oil cracking theory to develop an oil preservation index (OPI). The simulated temperature/thermal evolution degree is the key factor affecting crude oil preservation. OPI decreased by 0.230, 0.324 and 0.350, respectively, with VR_o increasing from <1.2%, 1.2%-2.0% to >2.0%. Crude oil with different properties often shows different preservation ability. Light oil, rich in saturated hydrocarbons with fewer branched chains and higher H/C atom ratio, shows stronger preservation ability in the early stage. But once the cracking threshold is reached, rapid cracking occurs. Heavy oil has more branched chains and heteroatoms due to the presence of non-hydrocarbons and asphaltene undergoes faster cracking in the early stage, and shows higher stability in the later stage. But most of the residue is solid bitumen and other macromolecule condensates. The depth limit of crude oil preservation was predicted by using the experimental results of thermal simulation in Manxi region, Tarim Basin. The depth limit of crude oil exploration in the southern Manxi region is 8 200 m.