Ningxia Old Oilfield Chang 8 Reservoir Favorable Areas Of Research

There’s hydrocarbon accumulation potential in Triassic C8formation of old oil fields of Ningxia, reservoirs of certain scale has not been found. Low level of exploration lead to the uncertainty of the accumulation controlling factors, figuring out the reservoir characteristics and forecast favorable target in the area has a big significance to oil field development and increasing of the back-up reserves. This paper has made a study on C8formation of Ningxia old oil field area, using sequence stratigraphy, sedimentology, petroleum geology, reservoir geology theory, combined drilling data, core, analysis of laboratory and logging data, analyzed the structural characteristics of the study area, depositional systems, depositional microfacies types and distribution systematicly, studied reservoir characteristics and the distribution characteristics of the sand body in-depth detailed, draw out the controlling factors of oil reservoirs, finally, made a a comprehensive analysis of tectonic, sedimentary, reservoir characteristics, to predict and evaluate the favorable target area. Conclusion include the following aspects:Completed3interface sand top structural map of the2sub-unit based on the hierarchical data, combined with the structural characteristics. The results showed that:overall, it tends to be higher in the north, lower in the south, higher in northeast and lower in the northwest. Gufengzhuang region developed several thrust fault with northwest-southeast extension, these faults provides a better place for hydrocarbon migration and storage. Local part developed small eminence and nosing structure, depth of burial is2302.0m～2699.6m, the surface altitude is-843.4m～-1115.6m, the bottom surface altitudeis-925.0m～-1214.7m.Carried out the sedimentary facies of sub-unit C81and82based on core and related data, combined with debris and logging data, finished microfacies analysis and mapping. The results showed that:the target layer developed a front delta-shallow lacustrine depositional system, sand body microfacies are mainly distributary channel, broadband-like with northwest to southeast extension, see some sand dam scattered in the distributary channel.Studied the characteristics of the reservoir rock, types and characteristics of reservoir pore, as well as the reservoir physical features of sub-unit C81, C82using well logging interpretation and core analysis data, drew the reservoir sand body isopach map. The results showed that:the reservoir rock are lithic arkose and feldspathic lithic sandstone, occasionally quartz sandstone, compositional maturity and textural maturity is generally low, porosity types include intergranular pores, intragranular dissolved pores, intergranular dissolution pores; reservoir distribution and characteristic is different in sub-units, contiguous is better in the NW-SE direction, heterogeneity is strong; reservoir physical property is generally medium-low in the porosity and low-especially low in permeability.Studied oil source, structure, deposition, reservoir and their control effect to the accumulation of the Chang8formation. The results conclude:(1)Studied area is at the western edge of the ancient lake basin, good oil generation conditions of C7and the adjacent layer, connected with the ancient lake basin are material ensure to form effective oil gathered region of the formation;(2)Structures controled the scope and scale of the crude oil gathering, local small anticline or nose uplift is the key of the oil gathering;(3)Reservoir sand body provides crude oil gathering place, river or dam facies with pore space of native or secondary porosity are potentially favorable areas for the formation of oil and gas accumulation;(4) Optimal configuration of the oil source, structure, sandstone, good physical properties and many other conditions in space is the basic conditions for hydrocarbon accumulation of the formation.analyzed reservoir characteristics and laws of oil and gas accumulation in C8layers, evaluated the quality of the reservoirs, predicted geological reserves. The results showed that:(1)Oil-rich area of C82reservoir is distributed in three regions, restricted by structure and lithologic factor, reservoir scale is smal, with low saturation, low porosity, extremely low permeability;(2)Oil-rich area of C81reservoir dispersed in four regions, restricted by lithology, structure, physical property, are also low saturation, low porosity and extremely low permeability reservoirs, one is a larger reservoir (estimated reserves of13,580,600tons) and one medium (estimated reserves of5,186,900tons), the rest smaller.By evaluating and optimizating, Chang81reservoirs is better than Chang82, it is recommended that favorable built-producing areas for our studing area are Production Y41,production H188in C81reservoirs and Production Y67-Y28.