khair, Elham Mohammed M. (Sudan University of Science & Technology) | Zhang, Shicheng (China University of Petroleum, Beijing) | Abdelrahman, Ibrahim Mustafa (Sudan University of Science & Technology)
The current study presents elastic properties model for Fulla Oilfield in northeast of Block 6 in south of Sudan. Due to the poor formation consolidation and relatively viscose fluid, reservoirs may predictably produce massive amounts of sand and numerous troubles were found in the field as a result of sanding. No documented researches were found to introduce good parameters for rock strength and rock failure conditions through the field. Therefore, an accurate technique for predicting rock failure conditions may yield good profits and improve the economic returns through preventing sand production from the formations. General correlations were presented to accurately describe rock strength parameters for the field; the work utilizes the application of the wireline porosities to be used as a strength indicator through the combination of rock mechanical theories with the characterization of Fulla oilfield. Log porosities (density, sonic and neutron) were calibrated with the core measured porosity, and the best matching porosity were correlated with the dynamic calibrated strength parameters by different correlations. The results support the evidence of the use of porosity as an index for mechanical properties; power functions were found more reliable than the exponential functions, and can be used with a high degree of confidence; also it is more accurate than the Shale Index model presented in previous work for same field; however, the result does not support the direct linear expression presented in the literature for other field due to the variations in the field conditions.
This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper IPTC 13636, "The Use of a Plume Modelling Study to Reduce the Risk of H2S Release in an Exploration Well to as Low as Reasonably Practicable (ALARP)," by J.G. Mcllroy, SPE, Petroleum Development Oman, originally prepared for the 2009 International Petroleum Technology Conference, Doha, Qatar, 7-9 December.
Liu, Bingshan (Research Institute of Petroleum Exploration and Development) | Zhou, Shi (CNPC Chuanqing Drilling Engineering Company Limited) | Zhang, Shunyuan (Research Institute of International Technologies of CNPC Drilling Research Institute)
The two main target formations of shallow horizontal wells in Sudan are Bentiu formation and Aradeiba formation. They are becoming more and more important with the exploration of oilfield, and they are all about or shallower than 1000m underground. The stratums are loose, so some measures are adopted to ensure the success of drilling operations: studying the stability of the borehole, optimizing the hole structure and casing program, establishing the drilling fluid system and its formulation.
We get the pore pressure, collapse pressure, and the fracture pressure by studying the formation pressure system using professional software upon the logging data. Study the relationship between the content of clay and the stability of borehole. It shows that the clay content has significant effect to borehole stability in Sudan. Then we analyze the collapse period of the upper stratums. The time window is about from 5 days to 7days. Based on the results and the study of the data of those wells drilled, the horizons of leakage and collapse are indicated. According this and the formation pressure, we optimize the hole structure and casing program. Finally, the KCl-polymer system is sifted as the drilling fluid. We determine the mud density according to the formation pressure first. Then the contents of KCl and the additives are indicated by experiments. According the experiments, the ideal percentage of KCl is form 6% to 8%, and the percentage of QS-2 in the drilling fluid using in field is from 3% to 4%. Now there are 5 shallow horizontal wells have been drilled in Sudan. The research achievements have been applied in the drilling operations. The average drilling cycle is about 17 days. Moreover, the hole diameter enlargement rate is decreased remarkably.
Stephen, Hiebert (Petroleum Development Oman) | Blonk, Bastian (Petroleum Development Oman) | Mazroey, Mohammed (Petroleum Development Oman) | Al-Harthy, Mohammed (Petroleum Development Oman) | Harris, Kester (Petroleum Development Oman) | Shuster, Mark (Petroleum Development Oman) | Al-Hadhrami, Mohsin (Schlumberger)
In the northwest area of Petroleum Development Oman's (referred to later in this paper as ‘PDO') concession, substantial oil volumes have been discovered in conventional structures trapping low permeability carbonates of both the Upper and Lower units of the Cretaceous Shuaiba Formation. However, since full-scale development of the area began, only a fraction of production has come from the Upper Shuaiba. Previous drilling campaigns targeting Upper Shuaiba have met with limited commercial success, because oil-charged reservoir occurs in thin pay (1-5m), and production test rates from the mostly vertical wells are generally less than 100 bbl/d. In late 2000, an exploration well was drilled on the crest of the Malaan structure, and similar to many previous tests in the area, encountered oil in several thin units of very low permeability (2-10 mD), but failed to flow at a sustainable rate. Subsequent reprocessing and inversion of the seismic, combined with a revised geological model which was partly based on experience of neighbouring operators, indicated the possibility of a higher porosity and permeability trend considerably down the flank of the Malaan structure. The trend is coincident with a top-lap truncation imaged on seismic, forming elements of a stratigraphic trap with the overlying Nahr Umr Shale.
In July 2003, the Malaan-2 well was spudded approximately 3 km northwest and 29m down flank of Malaan-1, and found significantly better reservoir quality. New logging while drilling technology (LWD) from Schlumberger, used for the first time in the world in an exploration well, was critical to maintain the horizontal well path in the best quality reservoir rock. The well has been tested and hooked up, and appears to have a stable production rate of over 1400 bbl/d net oil.
Seismic imaging shows that the best reservoir is coincident with an amplitude anomaly which extends more than 20km in a south-westerly arc, and which is independent of current structure. Forward modeling, incorporating all well data, has now allowed a match between synthetic and real seismic, and giving more confidence in the geologic model.
The trapping mechanism, and the factors controlling oil saturation, are not fully understood; the area has recently undergone regional structural tilting, and it is possible that the hydrocarbons are not yet in equilibrium. Several appraisal wells planned for 2004 will further delineate the extent of the accumulation and provide a better understanding of the trap. In a success case, the elements of this exploration play will be applied to other similar seismic trends already identified across northwest Oman.