Horizontal wells have been drilled extensively in recent years where several challenges have been faced such as increased cost, short well life, limited accessibility, uneven stimulation, less productivity, water production, etc. Although similar issues encountered in all reservoirs, tight reservoirs impose an extra difficulty given their complexity and inherited limited productivity. In order to optimize horizontal wells to overcome such challenges, an innovative technique was proposed and successfully implemented.
Initially a single well simulation study was conducted to determine and evaluate the effectiveness of using a dual completion string in a horizontal well with open hole across carbonate reservoir which generally suffering from rapid increase of water-cut due to high drawdown around heel. A review of literature and internal well cases were conducted to highlight the heel to toe effect and early water breakthrough issues. As a result a novel multi-zones completion technique was proposed and implemented (first time in the Middle East), this design comprises running a lower completion (LC) as isolation string and an upper dual completion, the hole heel will produce from the open hole (OH)-LC annulus through the short string (SS) and the toe will produce through LC through the long string (LS) stung-into LC. This design provided a method to choose the most appropriate horizontal section and demonstrated the value of having dual completions in terms of oil gain and water management as well as improved accessibility. The case presents an out of box solution where target reservoir was successfully tested through dual completion strings in same horizontal hole.
Production Segmentation Completion Technique (PSCT) was introduced. Field results supported the success of Dual Completion project providing future opportunity to optimize the production configuration of horizontal wells. Thus, reducing number of wells and increasing production. Execution of this project increased production by about 1.3 xs versus single completion well, accessing deeper horizontal areas, with an optimized cost in addition to time savings.
This new approach aims to encourage flow from both compartments of the wells with a dual completion configuration. This leads to less toe/heel effects. Also provides control on water coning which results in lost wells especially when high permeability zones exist at heel. Additional benefits include horizontal accessibility improvement, even and effective stimulation, reduced collision risk by minimizing boreholes and reduced overall well cost.
Application of this approach in early stages may be crucial to mitigate potential well issues that are difficult to cure later in well life. This complex and high profile project was executed against a background of limited time frame and resources. Project team demonstrated ability to adapt and succeed when presented by a truly unique challenge. To date, PSTC technique is the first to be implemented in ADNOC OFSHORE and the Middle East.