Abstract
Karstic-fault oil pools are a new type of carbonate reservoirs which is consisted of groups of large caves with high oil storage potential. In this study’s examinations of high-yielding wells, it was found that many valuable reservoirs relate to the drilling wells through fractures or karst caves, and it was not possible to determine the reservoir depths through the method of seismic prospecting precisely due to its poor vertical resolution. The conventional logs cannot be run in the case of no mud circulation due to leaking to the caves. If the depths of the reservoirs cannot be determined, then it becomes difficult to achieve long term and stable development of the oil resources in the reservoirs. The heat transfer between wellbore and formation during oil production processes was simulated by CFD. The Horner method was used for estimating the flow temperature during the stable production stage using the temperature curve measured after shut-in. This research presented a scheme which could be used to effectively determine the depths of karstic-fault reservoirs by static and flow temperature logs. The proposed method was applied to a well located in the Tahe Oilfield of the Tarim Basin. The application of the method will aid in deepening our understanding of the distribution of fault-karst reservoirs, as well as in supporting the future stable and sustainable high-yielding oilfield production of similar reservoirs.
Highlights
A new type of carbonate reservoir, referred to as karstic-fault systems, has been discovered in the Tahe Oilfield, Tarim Basin, in northwestern, China
High-temperature fluid flowed through the wellbore
Through the numerical simulations of the oil production processes, it was found that the well hole temperature measurements were related to the shut-in times
Summary
A new type of carbonate reservoir, referred to as karstic-fault systems, has been discovered in the Tahe Oilfield, Tarim Basin, in northwestern, China. It has been observed that after a period of production, the caves which are connected to the production wells tend to be replenished with oil from deeper deposits. At such times, it is urgent to determine the reservoir depths in order to update the understanding of the reservoir situations, as well as the development plans. It has been observed that large caves tend to generate “bright spots” in seismic images, which are produced by the high-reflection energy in a plane (Figure 1(a)) The positions of these “bright spot” seismic facies have been found to generally leak drilling mud, and the wells are characterized by high and stable oil production. The researchers believed that the oil had originated from the bottom of the karst cave [7]
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