Transverse Multi-Fracture Technique in Kitina Highly Deviated Off-Shore Wells

Abstract

Brownfield field have been defined as mature field in a state of declining production or reaching the end of their productive lives. Nevertheless these fields provide more than 50% of world's production as well as world's reserves and so it will be for next 20 years. For that reason revitalization of mature fields has to be a "must". The Kitina Field, offshore from Pointe Noire, Congo, is one such field. Deeper sands have been produced to economic depletion and, in order to maintain the economic operation of their valuable assets, alternative production intervals have been opened to production. Most of these low permeability reservoirs can produce at economic rates only with the application of hydraulic fracturing treatments in a multi-fractured well scenario. Accurate candidate selection, optimized treatment design, sound reservoir modeling of production forecast represent crucial and interdependent factors for successful economic evaluations. This paper describes the massive hydraulic fracturing campaign carried out between April and June 2007 on the Kitina 3A reservoir, offshore Congo. Eight hydraulic propped fractures were placed in three re-completed, cased-hole highly deviated wells with very encouraging production increases (stabilized production increase ranging from 2 to 3 times). The transverse multi-fracturing technique was adopted. This technique utilizes a series of packers and frac-ports that are sequentially shifted allowing continuous placement of more than one hydraulic propped fracture without shutting down the pumping equipment. All the aspects from candidate selection, pre-job design, on-site operations and post job evaluations with particular focus on the operational challenges encountered are described. Recommendations for the future applications of this stimulation technique are proposed. Furthermore, the challenging theme of forecasting mid-long term production profiles for horizontal, slanted and vertical multi-fractured wells is tackled. Different analytical and numerical models, approaching the task with various methodologies, were applied and tested to define the production profiles of the three candidate wells, which differ in terms of geometry and reservoir properties. On the base of the experience gathered on such wells, some general guidelines were drawn for a wider application. Introduction The Kitina Marine offshore field was discovered in 1991 and production start up was in December 1997. Originally, the field development considered the three deeper intervals that were developed via a peripheral water injection scheme and a crestal gas injection displacement process. After a quite significant initial rate (around 50,000 BOPD), the field declined quite rapidly and it was necessary the installation of gas lift valves on all wells. In 2005, aiming to reduce the inevitable rate decline, a new level was opened to production via the recompletion of three deeper wells into the shallower and low permeability 3A reservoir [Ref.1[. This interval is characterized by the presence of thin silt and shale layers that decrease the vertical permeability strongly. The 3A Sandstone reservoir was initially produced in natural flow between the end of 2005 and august 2006, although the three wells were completed with gas lift mandrels (Fig. 7, Fig. 8, Fig. 9). Due to the low permeability (2–7 mD), after first year of production, level 3A in Kitina field had progressively declining production heading to a marginal-economic scenario. At the beginning of 2007 the production was:KTM W6 ST - 160 BOPDKTM 107 - 130 BOPDKTM 111 - 300 BOPD

History Match and Reserve Evaluation of Hydraulically Fractured Wells: Low Permeability Field Case History

“…Due to the increasing oil price scenario in 2007, the three wells were hydraulically fractured in order to raise oil production [Ref. 1,2,3]. The stimulation operations were characterized by a high expenditure compared with the most common on shore treatments.…”