Abstract:
Gypsum salt rock is often associated with deep and ultra-deep oil and gas resources, and it is rich in a large number of salt resources. Due to the unclear description of the spatial distribution characteristics of gypsum salt rocks, it is easy to cause complex engineering accidents such as dissolution collapse, expansion and shrinkage during resource development, which will restrict the efficient development of oil, gas and salt resources. The Paleogene gypsum salt rock in 4th member of Shahejie Formation (Sha-4 Member) of Dongying Depression was analyzed based on seismic, well logging, well logging and geochemical data. The rock mineral characteristics and geophysical response laws were revealed, and the different scale gypsum salt rock identification methods were reviewed. Besides, the longitudinal evolution and plane distribution characteristics were clarified, and the sedimentary environment and development model of gypsum salt rock were reviewed. The results are as follows: ① The identification of the core size of gypsum salt rocks was mainly based on physical properties such as water absorption and expansion, soft properties, water solubility and salty taste. At the wellbore scale, the gypsum salt rocks had the special electrical characteristics of negative anomaly of spontaneous potential curve, low natural gamma value, low acoustic transit time value, high resistivity value. The gypsum salt rock location was determined by the expansion or contraction of the well diameter. The strong seismic reflection amplitude was used to calibrate and trace the spatial position at the well and region level. ② There were three typical sedimentary evolution cycles along the vertical orientation in gypsum salt rocks of Sha-4 Member in Dongying Depression. Gypsum salt rocks were distributed near the sedimentation center in the central and northern part of the depression. The lithology changed from clastic rock to carbonate rock and then to gypsum rock from bottom to top and from edge to center. ③ The formation of gypsum salt rocks was in high paleosalinity, arid paleoclimate, shallow paleowater depth, reducing salt lake environment, and the dry climate would cause precipitation reduction, resulting in shallow water and rising salinity in the lake. The minerals and halogenated ions were concentrated and crystallized. And the gypsum salt rocks strata easily formed at the bottom of the lake center. Ascertaining the sedimentary characteristics and development model of Paleogene gypsum salt rocks in Dongying Depression could provide guiding significance for the efficient development of deep and ultra-deep oil, gas and salt resources.