Multiple Transverse Fracturing in Horizontal Open Hole Allows Development of a Low-Permeability Reservoir in the Foukanda Field, Offshore Congo

Abstract

During the past decade, multiple transverse fracturing in horizontal wells has been applied so successfully in onshore low-permeability reservoirs that it is becoming the standard completion practice in many areas. The reasons for the success of this technique vary, but the two main reasons are related to the undisputed effectiveness of hydraulic fracturing as a production enhancement technique and the relatively low cost of pumping services in onshore areas. Success and industry eagerness for process/cost optimization have contributed to many technological improvements in the multistage completion process allowing sequentially executing several fracturing treatments in a single pumping operation. Nevertheless, the high direct and indirect costs and the risks associated with offshore operations have traditionally been limiting factors in spreading this technology to offshore applications. Sometimes, the misplaced perception of hydraulic fracturing as risky and costly operation prevented, rather than encouraged, its application in marginal offshore oilfields. Recent increases in oil prices and the success in onshore applications have encouraged the use of hydraulic fracturing in offshore applications. This study documents the successful effort of taking these techniques to the offshore environment. Transverse fracturing with multistage completion concept— with properly engineered design of well trajectory—can make the difference between the economic success or failure in the field development of low-permeability reservoirs. This study used multidisciplinary and integrated approach to design and execute the treatments, involving reservoir, production optimization, and fracturing engineers from the early stages of well planning to construction. The multilayer Foukanda field, located 52km offshore from Pointe Noire, Congo, has a low permeability and virgin target that was considered noncommercial after discouraging results of two wells. Based on the production results of three cased-hole wells in an analogous field where multiple propped fracturing was applied, the operator decided to drill an open-hole horizontal well that was to be multi-fractured. The initial 90 days average production of this Foukanda well was more than 2500bbl/day. This production rate was double the simulated rate of a vertical well and opened a wide range of further developments both in Foukanda and in other analogue fields in the offshore Congo. Introduction The Foukanda Marine field is located, 20 km to the north of the Kitina platform and 52km to the west of the city of Pointe Noire. Average water depth is around 100 meters. The field was discovered in 1998 by the well FOKM-1. Production started on June 2001. In the same year one well was drilled in the reservoir D but, due to very poor reservoir characteristic this level was abandoned and the well was recompleted on the shallower reservoir B4. The low permeability reservoir D (less than 10 md) was therefore abandoned and only the reservoir B4 and B7 put on production. In the first months of 2007 Foukanda field had a production potential of about 3000–3500 bopd with 6 producer wells (5 in the reservoir B4 and 1 in the B7) and 2 injector wells (2 in B4 and 1 in B7).

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