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Abstract Fula is a heavy oil field located in Muglad basin in Sudan. Aradeiba reservoir in the field consists of highly heterogeneous sandstone that is thinly bedded, unconsolidated, bearing typical heavy oil. Bentiu reservoir is composed of massive sandstone, unconsolidated and traped very high viscous oil. Production performance of vertical wells indicates that the reservoirs are facing problems of low productivity, bottom water conning and sand production. In his circumstance CNPCIS set itself a daunting task of tripling the production in less than a year.
Horizontal wells were considered as best option for improving the productivity in this small to medium sized heavy oil field, and controlling the sand production due to low drawdown pressure and increased exposure the reservoir.
This paper discusses about comprehensive geological study , identification of target oil pools, well design, selection of fit for purpose technologies and the complete well placement cycle including detailed analysis on the drilling and steering challenges while placing horizontal well through reactive shales and channel sand environment. The paper also discusses about various completion strategies , the results of well placement, value of using new technology , lessons learnt and cost /production analysis.
Team work, communication, knowledge sharing and deployment of fit for purpose technologies has resulted in a five fold increase in production through horizontal wells compared to vertical wells with no sand production. The paper illustrates how integration of different disciplines led to successful well placement, enhanced production with sand and water management in heavy oil environment.
Introduction Fula Oilfield is located on central structutre belt of Fula depression in Muglad Basin which consists 3 main blocks -Fula-1, Fula Central and Fula North. Three reservoirs have been found by the exploratory and appraisal wells in the area. Bentiu formation is the main reservoir in Fula Oilfield with massive lose sand and average viscosity is about 1536.39 cp at 500C. Aradeiba is the second reservoir with stratified unconsolidated paysand and average viscosity around 450 cp at 500C. Bentiu reveroir is prone to sand production and water break through very quickly and Aradeiba reservoir is prone to serious sand production and very low output rate in conventional vertical wells. In order to prevent sand production from both reservoirs, to delay water production from Bentiu formation and increase productivity and enhace the reservoir recovery factor operator decided to drill horizontal wells. Another important driving force behind drilling horizontal wells is to improve the light oil production from Aradeiba reservoir that is crucial for blending and transporting the heavy oil from Bentiu reservoir through the pipeline. Seven horizontals have been drilled, out of which four of them are in Aradeiba formation and three are placed in Bentiu fiormation. The production performances of all the wells are extremely good year to date.
Geological Setting and Stratigraphy Being a rift and Cretaceous sedimentary basin, Muglad basin is located south of Republic of Sudan. Tectonics was complicated by faulting and continuous fault movement and several sub-basins formed result in this large numbers of tensional faults. Structures within these depressions show significant variations in age of formation, complexity and size.
The result of regional stratigraphy study indicates a major East Africa rift basin appeared and developed in the Late Jurassic to early Cretaceous. Early rift sediments interbedded with coarse rift clastics derived from surrounding uplifted basement source rocks.
Several types of continental depositional environment may had existed in different areas including fluvial and lacustrine during the Cretaceous and younger period. Fula Sub-basin is located in north part of Muglad Basin and consists of 5 structure belts namely south step-faulted belt, south depression, central structure belt, north depression and north step-faulted belt. Several oilfields like Moga, Keyi and Jake have been discovered after Fula field in Fula Sub-basin recent years. Located in Central Structure Belt of the sub-basin, Fula is one of the earliest oilfield put into production.
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