Quantitative recognition and petroleum geological significance of interlayers in coastal sandstone reservoirs: A case study from the Donghe Sandstone in the Hade Oilfield, Tarim Basin, NW China

Buried coastal sandstones would be of high-quality hydrocarbon reservoirs. Controlled by deposition and diagenesis, coastal sandstones mixed with muddy and calcareous materials are usually low in porosity and permeability and small in layer thickness. These impermeable interlayers act as baffles and barriers between flow units and are crucial in hydrocarbon development. Donghe Sandstone in the Hade Oilfield of Tarim Basin, NW China, belongs to coastal clastic reservoirs of high oil productivity. Following nearly 30 years of development, the distribution of remaining hydrocarbon resources is affected by the muddy, calcareous, and marlaceous interlayers. Taking the Donghe Sandstone as an example, a quantitative recognition method of interlayers in coastal sandstone reservoirs is proposed in this paper. Based on cores from 26 wells, the sensitive conventional log curves of different interlayers, namely the natural gamma-ray (GR), density (DEN), compensated neutron (CNL), and acoustic (AC), are extracted by the Extreme Gradient Boosting (XGBoost). Multi-mineral model (MMM) is used to calculate continuous curves for muddy, sandy, and calcareous contents by the mentioned sensitive logs. A set of quantitative standard system is established for identifying muddy, calcareous, and marlaceous interlayers based on their respective contents. The types of interlayers are identified across all vertical wells. The interlayers exhibit lateral continuity at the top of each bed-set. Interlayers are currently more developed in the slope region than in the coastal region. Muddy and marlaceous interlayers are more developed at high relative sea-level, while calcareous interlayers are more developed at low relative sea-level. The extended interlayers at the top of BS6 lead to two different oil-water contacts in the Donghe Sandstone. The proposed quantitative recognition method for interlayers provides valuable insights into the exploitation potential of petroleum systems in the Donghe Sandstone of the Hade Oilfield. The flexible and easy-to-use method can be applied to other marine sandstone reservoirs or similar formations.