SEDIMENTARY CHARACTERISTICS OF A NEAR-SOURCE STEEP SLOPE DELTA AND THEIR CONTROL OVER OIL ACCUMULATION: AN EXAMPLE FROM SHA-4 FORMATION, KL OIL FIELD IN LAIZHOU BAY DEPRESSION

Sedimentary characteristics of a fan delta in the 4th Member of the Shahejie Formation located on the south slope of the Laizhou Bay Depression are studied, aiming at finding out the major reservoir of the fan-delta sand of the KL Oilfield. Data of wall sample, thin slice and scanning electron microscope are used for the purpose. Reservoir controlling factors and reservoir space types are also discussed. Results suggest that the fan delta was a retrogressive one developed in a warm and dry climate, consisting of brown conglomerate, green gray tuffaceous gravel sandstone, colored gravel sandstone, and gray coarse sandstone from the bottom up, with thin layers of tuffs locally. Clastic components including quartz, feldspar and volcanic rock debris are cemented by muddy, tuffaceous, and dolomitic interstitial materials. Both the deposition and diagenesis control the formation of reservoir. Gravel sandstone and coarse sandstone deposited in the fan delta front are well sorted, and their pores are dominated by the type of intergranular, followed by dissolution pores. The diagenetic dissolution can improve the reservoir space obviously. The fan-delta plain sediments, however, are poorly sorted with less intergranular pores. The dissolution effect is not well developed under heavy compaction, instead, the accumulation space is further deteriorated. Based upon the distribution pattern of the deposits on the southern slope, it is concluded that the gravel sandstone deposited in front of the fan delta is the most effective reservoir and exploration target.