Multi-Lateral technology was selected in SPDC as one of its strategic cost leadership initiative to drive down the development costs of its hydrocarbon assets. Its main objective was to reduce well construction costs by 30 – 40% in terms of unit footage costs and unit development costs and to increase string months available per rig. The technology implementation was set within legislative requirements peculiar to the area and its reservoir geology, which constrained the available options.
To date five level 6 multi-lateral wells have been successfully drilled and completed while a sixth one was aborted due to a junction installation failure. Two of the wells were Deep Set Splitter (DSS) installations in the same field while the others were Formation Junction (FJ) applications in two different fields. Field execution for the Formation Junction wells encountered significant challenges, which resulted in several innovative approaches including design and procedural modifications to achieve success. Commercial improvement was also observed as the implementation progressed.
This paper presents the application of level 6 multi-lateral technology and it's impact in SPDC. It reviews the concept selection, engineering planning, risk analysis and mitigation for the wells. It dwells on the technical experiences from the execution phase with a special focus on the failed attempt. It also presents learnings and best practices from the technology implementation with recommendations for future applications in the industry.
Introduction
Multi-lateral well technology provides a means to reduce well costs in a multiple well target development, or increase the value of the planned wells. In addition to boosting well productivity, multi-lateral drilling can also tap bypassed reserves. As an industry wide application, it has proven value through enhanced oil recovery, accelerated production and improved NPV from reduced drilling CAPEX.
By definition, a multi-lateral well is one that allows two or more drainage points through either deviated or horizontal wells in the reservoir, connected back to a single main bore from a single site[1]. The technology is a viable development strategy for new fields. In some cases the technique can also make marginal fields economical due to more cost and production efficient wells. ML classification is based on the TAML system from level 1 to level 6, which refers to the nature and type of hydraulic seal required at the junction creation point, and is not a scale of increasing complexity.[2].
In Shell Nigeria ML technology was proposed in 1998 as one of its strategic cost leadership initiatives. The primary business driver was reduction in hydrocarbon development costs with the prospect of delivering three horizontal laterals at the price of two (i.e. 1 ML well=1.5 Hz well). This was in addition to indirect but obvious benefits such as savings in location construction, land acquisition, flow line construction, reduced environmental impact and exposure to host communities. A multi-disciplinary project implementation team was set up and empowered to;Define an ML implementation strategy based on low risk and low costSelect a technology applicable for land, swamp and offshore operationsEvaluate both technically and commercially existing ML technologies and if necessary to get the industry to develop new technologies.Drill and complete the first ML well by the year 2000.
Wells Design
Sub Surface Considerations
Hydrocarbon occurrences in the Niger Delta are generally associated with stacked reservoir sequences primarily consisting of channel and shore face deposits that are for the most part hydrostatically pressured. The clastic depositional environment consists of geologically young and unconsolidated high-permeability sands and relatively plastic shales. The fields are usually faulted by conjugate systems of synthetic and antithetic faults.
