Research To Oil Reservior Formation Regularity In West Exploration Area Of Fengfuchuan Oil-field, North Shanxi

Studying the regularity of hydrocarbon accumulation is the foundation of the oil/gas exploration and the important basis for exploration strategy. The practical activity of oil/gas exploration was generaly scientifically guided by studying to the oil/gas reservoir forming conditions, controlling factors and hydrocarbon enrichment rule as well as the reservoir distribution principle. Fengfuchuan Oilfield, located in the eastern ordos basin, is a new area discoved by Qinghuabian Oil production plant in the earlier time of this century. Located in the western region of Fengfuchuan oilfield, the studied area shows complex hydrocarbon accumulation condition. This paper made extension and continuous exploration reaerch to area near old oilfield by applied modern hydrocarbon accumulation theory and method on the basis of predecessors’ research results. By abundant stratigraphic classification and correlation, petroleum geology such as reservoir structure and sedimentary facies together with sand body distribution and hydrocarbon accumulation were comprehensive studied to determine the main controlling factors of hydrocarbon accumulation. Oil/gas enrichment regularity and exploration target were also selected and evaluated and favorable exploration blocks were chosed for providding data for oil/gas exploration in the next step.Studies have shown that Yanchang Fm in the studied area presents tectonic framework with alternating uplifts and depressionsin on tectonic background of a big slope with east high but west low of the ordos basin. The area locally developed smaller tectonic peak. Obvious changes have taken place in the sedimentary period of Yan’an Fm. The tectonic pattern with east high-west low of Yanchang Fm. changed into the structure with northeast high-southwes low of Yan’an Fm. The thickness of Chang6, Chang 4+5 and Chang 2 of Yanchang Fm. are more stable with small horizontal change showed relatively stable sedimentary environment and litter water depth variation. It was advantageous to the oil/gas generation and accumulation. Sedimentary facies in the study area are mainly delta front and delta plain facies,which developed five channel sand bodys in the direction of northeast to southwest. The main channel sand body distributed wide in the area with large thickness. The ancient geomorphic unit during the sedimentary period of Yan’an Fm. is mainly composed of slope and the valley with highlands in northern, ancient river in south, slope and gully in the middle. Snadstone of Yanchang Fm. in the study area mainly is composed of lithic feldspathic sandstones, feldspathic lithic sandstones and feldspathic sandstones. Clay minerals of sandstone is mainly chlorite. The pore types of sandstone mainly primary intergranular pore and secondary dissolution pores. Physical property of sandstone is bad which belongs to low porosity of 6% to 15% and low permeability generally between 0.1-5 x 10-3 um2. The plane distribution of reservoir physical property is consistent with the distribution characteristics of sand body. Yanchang reservoir sandstone compaction and cementation made reservoir density and becme reservoir featured with low porosity and low permeability. Late effects of dissolution and fracture on low permeability reservoirs has obvious effects on reservoir physical property.The area has experienced two times of hydrocarbon accumulation. The early reservoir was damaged due to the late tectonic movement which resulted in secondary hydrocarbon migration. The earlier reservoir formation took palced after dissolution but before compaction of reservoir sandstone. The hydrocarbon accumulation was controlled by structure. Oil accumulation and the reservoir compaction process took placed simultaneously. Oil/gas accumulation was gethed mainly in dissolution pores withich were the main storage space of the lithologic reservoir.There were many factors controlling oil/gas reservoir formation. The source rocks controlled the oil /gas supply and hence influence reservoir distribution. Distribution and connectivity of superimposed sand body, low amplitude structure and reservoir physical properties are the basic rules of oil/gas enrichment and reservoir fromation in the region. Reservior with different horizon shown differnet factors of controlling oil/gas accumulation with different exploration strategy. Exploratio to reservior of Chang4+5 and Chang 2 should pay attention to the lithology reservoir with low amplitude structure. The key targets for Chang6 reservoir exploration should pay attention to lithologic trap composed of sand bodies with large areas superimposed with dissolution and fracturation.Eight favorable exploration target zones in the study area were choosed. The scope belt about two kilometers on each side along the well Ding 41 to Ding 28 is the key zone for oil/gas exploration to Yanchang Fm reservior. The ancient river valley and the slope on both sides of valley eveloped at Renjianggou- Guozhuang area is favorable exploration area for palaeogeomorphic reservoir of Yan’an Fm.