An engineer’s toolbox holds a wide variety of completion options including open-hole, perforated case-hole, slotted liners, perforated liners, inflow control devices (ICDs), inflow control valves (ICVs), autonomous ICDs (AICDs), wire wrapped or mesh screens, gravel packs, and FracPacks. These can all be applied to either vertical, deviated, horizontal or multi-lateral wells. The big question arises: how can I choose the best completion design for my wells?
Proper completion selection requires knowledge of the completion impact on the production and economics over the well lifetime. Reservoir simulation software is typically used to estimate field production; however, it over-simplifies representation of the completions because conventional reservoir simulators historically focus on flow in porous media rather than wellbore hydraulics. As a result, the wellbore is usually represented as a set of sinks in grid blocks connected by nodes. To model a simple well with annulus and zonal isolation, the engineer must use keywords to describe a network of a few hundred nodes and assign proper correlation to each one. This process is very tedious and prone to errors. In addition, reservoir simulators do not provide a conventional interface for viewing the resulting flow inside wells.
The wellbore hydraulics simulator can be used alone as a screening tool to select the best completion design. However, this can only be done as a snapshot in time and does not reflect the influence of the completion on the long-term reservoir behavior.
All this can negatively impact the completion selection process, and the economics of the asset1, especially when controlling unwanted water or gas influx.
Integrated Wellbore and Reservoir Modeling
An integrated reservoir-to-completion-to-wellbore model that accounts for dynamic interactions of well completion and reservoir over well lifetime allows for an optimum selection of well completion. The use of a wellbore simulator fills the gap between commercially available reservoir simulators (Nexus®, QuikLook®) and lift optimization software from Petroleum Experts (Prosper®) based on its ability to capture flow through various completions and create feedback to reservoir performance. This integration (Figure 1) combines reservoir deliverability with completion flow performance enabling an easy modeling of well-reservoir behavior. It also allows for collaborative workflows where the reservoir engineer sets up a model in a reservoir simulator, and the completion/production engineer uses the completion-focused software to evaluate well-reservoir combined performance over time as depicted by Figure 2.
Well Completion Selection, Design and Optimization Methodology
Halliburton has applied a simple methodology (Figure 3) for design and selection of complex well completions. This methodology couples the wellbore and reservoir simulators in a series of eight basic steps as follows:
i. Data gathering
ii. Reservoir model prototype
iii. Well type design
iv. Initial well completion selection and design
v. Sensitivity analysis
vi. Well completion optimization
vii. Peer Review and proposal generation
Initially, all data needed for modeling the wellbore and reservoir is gathered, a reservoir model is built and the well schematic is defined. With these basics in place, the well completion is selected and designed using the near-wellbore model. A sensitivity analysis is then conducted using the wellbore simulator coupled with the reservoir model to investigate the effect of the completion design on the well’s production and economics. During this step several completion types can be studied for selection purposes, and if one type is selected, the parameters are optimized using the integrated model until requirements are met. The process is then peer-reviewed, and then the proposal is generated and ready to be executed.
Application of Methodology
This workflow has been extensively used in several applications worldwide with great success. Figure 4 depicts a case in which water cut was forecasted to rise significantly due to strong water-drive and water re-injection for pressure support. The integrated model was used to simulate water and oil production for the two top well completion choices (stand-alone screens (SAS) and ICDs). ICDs were selected as the best completion strategy with an optimized configuration of 22 ICDs with 10 swellable packers. The optimum design led to an increased cumulative oil production while minimizing water production compared to the SAS alternative.
A Simplified Approach with Great Benefits
The methodology of using coupled reservoir and wellbore simulators provides the most accurate and efficient well completion selection, design and optimization process. This leads to higher production and better economics by minimizing long-term production problems.
1 SPE 125251. “Coupled Completion and Reservoir Simulation Technology for Well Performance Optimization” Marcel A. Grubert, Jing Wan Sartaj S. Ghai, Silviu Livescu, William B. Brown , Ted A. Long (ExxonMobil Upstream Research) SPE Annual Technical Conference and Exhibition, 4-7 October 2009, New Orleans, Louisiana
2 SPE 104078. Ouyang, L. B., & Huang, W. S. (2006, January). “Case studies for improving completion design through comprehensive well performance modeling.” International Oil & Gas Conference and Exhibition in China. Society of Petroleum Engineers.
3 SPE 139435. Thornton, K., Soliman, M. Y., & Jorquera, R. (2010). “Optimization of Inflow Control Device Placement and Mechanical Conformance Decisions Using a New Coupled Well-Intervention Simulator.” SPE Latin-American and Caribbean Petroleum Engineering Conference, Lima, Peru. 1-3 December.