Quantitative Investigation of the Compaction of Mid‐Deep Sandstone Reservoirs in the Kaiping Sag, Pearl River Mouth Basin

ABSTRACT Significant hydrocarbon discoveries have been achieved in deep‑water and mid‐deep intervals in the Kaiping Sag, Pearl River Mouth Basin. Nevertheless, the mechanisms of the differential compaction and its reservoir‐controlling effects on sandstones across various structural belts remain poorly constrained, hindering precise prediction of high‑quality mid‐deep reservoirs. On the basis of petrographic, grain‐size, x‐ray diffraction, core porosity–permeability, and formation temperature–pressure data from 10 wells spanning the interval from the Wenchang Formation to the lower Zhujiang Formation, we adopted the Scherer original‑porosity model and back‑stripping inversion method to quantitatively calculate the compactional porosity loss (COPL) and cementation porosity loss. We systematically characterized the differential compaction patterns, major controlling factors, and their impacts on the pore‐system evolution. The results show that (1) the burial depth and overburden pressure are the primary controls on compaction; the clastic composition is the key depositional factor; the geothermal conditions promote chemical compaction; and the cement properties further regulate the porosity reduction. (2) The compaction intensity varies greatly among the structural belts: The shallow‑buried KPA Belt (structural belt) experiences weak compaction and has well‑preserved primary pores. The porosity reduction in the KPB Belt (structural belt) is jointly controlled by compaction and cementation. The moderate maximum burial depth of the KPD belt (structural belt) constrains the compaction intensity, and the dissolution, driven by the high geothermal gradient, also provides secondary‐pore compensation. The deeply buried, high‑pressure KPC belt (structural belt), with poor sorting, exhibits the strongest compaction, and secondary dissolution pores dominate the reservoir space. (3) Two critical compaction‑evolution depth thresholds were identified. At 2750 m, primary pores largely disappear. Above this depth, primary pores dominate, and the porosity decreases rapidly via compaction. Between 2750 and 3700 m, primary pores diminish, whereas secondary dissolution pores continuously develop. The depth of 3700 m marks the lower limit for chemical‑compaction equilibrium. Below this depth, the COPL stabilizes, and secondary pores dominate the reservoir storage. This established compaction‑evolution model for the mid‑deep sandstones provides theoretical support for reservoir evaluation and exploration targeting of deep‑water mid‑deep reservoirs in metamorphic core complex type sags in the South China Sea.