Africa (Sub-Sahara) Oil samples have been recovered in the FAN-1 exploration well, being drilled offshore Senegal. Elevated gas and fluorescence were encountered in a shallow secondary target, and the presence of oil was confirmed by an intermediate logging program. Oil samples from thin sand were collected by a wireline formation tester for further analysis. The well will be deepened to a planned total depth of approximately 5000 m. Cairn is the operator (40%), with partners ConocoPhillips (35%), FAR (15%), and Senegalese national oil company Petrosen (10%). A drillstem test of BG Group's Mzia-3 well--located in Block 1, offshore southern Tanzania, at a water depth of around 1800 m--reached a maximum sustained flow rate of 101 MMscf/D of natural gas. The Mzia prospect is a multilayered field of Upper Cretaceous age with a gross gas column estimated at more than 300 m.
Africa (Sub-Sahara) Eni started production from the West Hub development project's Mpungi field in Block 15/06 offshore Angola. The startup follows the project's first oil from the Sangos field in November 2014 and the Cinguvu field last April. Mpungi will ramp up West Hub oil production to 100,000 B/D in the first quarter from a previous level of 60,000 B/D. The project also includes the future development of the Mpungi North, Ochigufu, and Vandumbu fields. Eni is the block operator with a 36.84% stake. Sonangol (36.84%) and SSI Fifteen (26.32%) hold the other stakes.
Africa (Sub-Sahara) Kosmos Energy has made a significant deepwater gas discovery off Senegal. The Guembeul-1 well in the northern part of the St. Louis Offshore Profond license in 8,858 ft of water encountered 331 net ft of gas pay in two excellent-quality reservoirs, the company reported. The results demonstrate reservoir continuity and static pressure communication with the Tortue-1 well, which suggests a single gas accumulation. The mean gross resource estimate for the Greater Tortue complex has risen to 17 Tcf from 14 Tcf as a result of the Guembeul discovery, the company said. Kosmos, the operator, has a 60% interest in the well. Timis (30%) and Petrosen (10%) hold the remaining interest. In Salah Gas has started production from its Southern fields in Algeria.
Tan, Qiang (China University of Petroleum) | Liang, Jiwen (Zhanjiang Branch of China National Offshore Oil Corporation) | Luo, Ming (Zhanjiang Branch of China National Offshore Oil Corporation) | Zhang, Chao (Zhanjiang Branch of China National Offshore Oil Corporation) | Weng, Haoyang (China University of Petroleum)
China’s low permeability oil and gas reserves are abundant and widely distributed, which has become an important target for exploration and development. Formation damage is prone to occur during drilling in low permeability reservoirs, and it is difficult to recover effectively in production. Therefore, to protect reservoirs, underbalanced drilling has become a common drilling technique in reservoir stratum of low permeability oil and gas fields. Because of the low support force of drilling fluid column pressure in the process of underbalanced drilling, if the formation strength is weak or subjected to strong in-situ stress, it is prone to instability and cause drilling complex problems. According to the reservoir core mechanics experimental results and geo-mechanical data of some low permeability oil and gas fields in western South China Sea, a feasibility evaluation model of underbalanced drilling in horizontal wells was established. Based on this model, underbalanced drilling feasibility and underbalanced limit pressure difference were analyzed for horizontal wells in Huangliu group of D13 gas field, Weizhou group of W11 oilfield and Zhuhai group of W10 gas field respectively. The calculation shows that underbalanced drilling can be used basically in the horizontal wells of above reservoirs, but the magnitude of underbalanced pressure difference is greatly affected by the in-situ stresses and formation strength. The analysis results can guide underbalanced drilling design in horizontal wells of low permeability reservoirs in different blocks.
Low-permeability oil and gas fields refer to oil and gas fields with low reservoir permeability and poor production capacity that need to be taken stimulation to maintain normal production. China's oil and gas industry standard ”assessment methods for oil and gas reservoirs” (SY/T 6285-1997) stipulates that reservoirs with permeability below 50×10−3 μm2 are low-permeability reservoirs (Zhao et al., 1998). Low-permeability oil and gas fields play an important role in the development of oil and gas in China. At present, over 50% of China's remaining proven reserves of oil and gas are low-permeability reservoirs (Hu, 2009; Tang et al., 2013). Compared with conventional oil and gas reservoirs, low-permeability oil and gas fields require the introduction of more advanced technologies in the exploration and development stage. Such as four-dimensional seismic exploration technology, reservoir detailed description and initial microstructure analysis technology, new crack identification and fracturing technologies, horizontal wells and multi-branch well technology, slim hole drilling technology, and underbalanced drilling technology, all of these are commonly used technologies in low-permeability oil and gas fields (Zhang et al., 2009; Wang et al., 2001).
According to the analysis on the geology characteristics and drilling history of Beibuwan Basin in western South China Sea, this paper went through the reasons of poor dillability, and summarized the exploration and application in rate of penetration (ROP) optimization technology in western South China Sea. Incorporating with the experiences acquired from several wells recently drilled in Beibuwan Basin, a set of ROP optimization scheme which is suitable for the poor drillability formation in this basin was introduced, meanwhile a novel polycrystalline diamond compact (PDC) bit was also developed. Therefore, a series of ROP optimization solutions for Beibuwan poor drllability formation was proposed. Field experience recorded significant optimization of ROP in poor drillability formation in Beibuwan Basin. This novel technology has played an important role in drilling cost control in western South China Sea, and can serve as reference for future drilling operation on similar formations.
This paper was prepared for presentation at the 1999 SPE Asia Pacific Oiland Gas Conference and Exhibition held in Jakarta, Indonesia, 20-22 April1999.