Research On The Characteristics Of High Quality Reservoir From Lower Ordovician In The Bozhong 28-1 Oilfield

BZ28-1 oilfield is located in the central position of Bonan low uplift, which was discovered in 1980 s, producted in May 1989,and at present 20 wells have been drilled. Lower Ordovician carbonate reservoirs have good oil and gas shows or industrial oil and gas flow, as one of the main oil producing stratigraphy in BZ28-1 oilfield. It has the characteristics of low matrix porosity and well developed fracture.After a large number of research,it is found that this oilfield is currently facing problems of increasingly prominent contradictions between static data and dynamic information, which affected the adjustment of oilfield development. The reason is that the characteristics and spatial distribution of high quality reservoirs of target layer have low-level study,which led to main controlling factors of high quality reservoirs and fractures have none clear understanding.For that, based on analysis of the target layer cores, cuttings, sheets and logging data,using macroscopic and microscopic method to determine carbonate stratigraphic framework of target layer,analyzesing it sedimentary environment. The characteristics of high quality reservoir lithology, physical properties and reservoir space characteristics,characteristics of reservoir properties and spatial distribution were studied. Studies produce results that carbonate rock of target layers have undergone several uplift and subsidence in the formation process, leading to generate some stratigraphic unconformity in Lower Ordovician.Yeli-liangjiashan stratum in Lower Ordovician is successive deposition and small-scale transgression. It mainly deposits dolomitic flat in Yeli formation; Liangjiashan formation mainly develop dolomitic flat, mud flat and lime-mud flat, etc. Objective reservoirs include the types of pore-fracture type, fracture-pore and fracture type, various types of reservoirs on the log have obvious characteristics.Combined with oil test data,used the method of sonic jump,dual lateral resistivity and crossplot of porosity and water saturation to qualitative and quantitative identify fractures distribution characteristics of reservoir.It can be seen from the recognition results that fractures are developed in each interval, have a great contribution to their porosity and permeability of the reservoir. Therefore, the studied reservoir is formed by complex systems by fracture, not a simple matrix pore system.Combining production reality,the targeted high quality reservoir is that the porosity is greater than 3%, permeability is greater than 5×10-3μm2.The formation of high quality reservoirs affected by many factors, mainly including sedimentation, diagenesis and tectonic. Deposition produced no contribution to matrixporosity.In diagenesis process, the target layer is mainly improved by syngenetic dissolution,meteoric dissolution and dolomitization. But it also is damaged by cementation, compaction,cavity filling and dedolomitization. It can be seen from the sheet that the damaging effects of diagenesis is much larger than amelioration, as a result the formation of the contribution of the diagenesis reservoir quality is not great.In tectonic side,target layer in the study area distributed a large number of faults and fault associated fracture, which result in the formation of a complex fracture systems, filled degree is not high. The reservoir which is transformed by fractures, those porosity and permeability all has been greatly improved, formed the high-quality reservoir.