Lateral Contrast and Prediction of Carboniferous Reservoirs Using Logging Data in Tahe Oilfield,Xinjiang,China

Valuable industrial oil and gas were discovered in the formations of Ordovician, Carboniferous and Triassic of the Tahe （塔河） oilfield, Xinjiang （新疆）, China. The Carboniferous formations contain several oil- and gas-bearing layers. The lateral distribution of Carboniferous reservoir is unstable, and thin layers are crossbedded. This makes it difficult to do lateral formations＇ contrast and reservoir prediction, so it is necessary to develop a method that can achieve reservoir lateral contrast and prediction by using multi-well logging data and seismic data. To achieve reservoir lateral contrast and prediction at the Carboniferous formations of the Tahe oilfield, processing and interpretation of logging data from a single well were done first. The processing and interpretation include log pretreatment, en- vironmental correction and computation of reservoir＇s parameters （porosity, clay content, water saturation, etc.）. Based on the previous work, the data file of logging information of multi-well was formed, and then the lateral distribution pictures （2D and 3D pictures of log curves and reservoir parameters） can be drawn. Comparing multi-well＇s logging information, seismic profiles and geological information （sedimentary sign）, the reservoir of the Carboniferous in the Tahe oilfield can be contrasted and pre- dicted laterally. The sand formation of Carboniferous can be subdivided. The results of reservoir contrast and prediction of the Carboniferous formations show that 2D and 3D pictures of multi-weU reser- voir parameters make the lateral distribution of reservoir and oil-bearing sand very clear, the connectedness of the reservoir of neighboring wells can be analyzed, and five sand bodies can be identified based on the reservoir＇s lateral distribution, geological information and seismic data.

Characteristics of Volcanic Reservoirs and Hydrocarbon Accumulation of Carboniferous System in Junggar Basin, China

The Carboniferous volcanic reservoirs in Junggar Basin contain rich hydrocarbon resources,implying a great exploration potential,so that they have become a key replacement target for“three-dimensional exploration”.The study on the Carboniferous volcanic reservoirs and their hydrocarbon accumulation elements is significant for clarifying the orientation for exploration.In this paper,based on 37 reserves reports and 3200 reservoir test data,the Carboniferous volcanic reservoirs in Junggar Basin were discussed from the prospective of lithology and lithofacies,physical properties,reservoir types,main controls on hydrocarbon accumulation,and hydrocarbon accumulation patterns.It is found that the Carboniferous in the basin is mostly in the multi-island ocean-volcanic island arc structural-sedimentary environment,so it is geologically eligible for forming in-situ volcanic reservoirs.The volcanic rocks are:(1)mostly distributed along deep and large faults,with the lithology and lithofacies controlled by volcanic architectures;(2)dominantly lava,followed by volcaniclastic lava and volcaniclastic rock;(3)distributed in the periphery of hydrocarbon-generating sag and within the source rocks horizontally,and concentrated in the weathering crust at the top longitudinally,possibly leading to reworked weathering crust reservoir;and(4)liable to form inner reservoirs.The volcanic reservoirs can be concluded into four hydrocarbon accumulation patterns,i.e.,self-generating&self-storing in paleo-uplift and vertical migration,self-generating&self-storing in paleo-uplift and lateral migration,young-generating&old-storing in fault zone and vertical migration,and young-generating&old-storing in paleo-uplift and lateral migration.Future exploration will focus on the effective source rock development and hydrocarbon supply zones and the selfgenerating&self-storing and young-generating&old-storing patterns.The exploration prospects are determined to be the Ludong-Wucaiwan-Baijiahai slope belt and the southern slope belt of the Shaqi uplift(self-generating&self-storing pattern)in eastern Junggar,and the fault and nasal arch zone at the northwestern margin and the nasal arch zone(deep and large structure)in the Luxi area(younggenerating&old-storing pattern)in western Junggar.