Summary
Equalizer production systems and inflow control devices are used to mitigate water or gas-coning problems for mature fields. We have developed new modeling methods to simulate equalizer and interval control valve (ICV) performance in full-field multimillion-cell reservoir models under a parallel computational environment.
The authors present single-well performance predictions with and without an equalizer, and the results are significantly different in some cases. Full-field modeling with equalizers and ICV controls for several examples has been conducted. In such cases, many individual wells would have significantly improved performance. At full-field level, however, using equalizers or smart well applications without total field optimization would not improve performance much, for reasons discussed in this paper.
The frictional pressure loss across an equalizer can be considered as a skin, and we have developed an analytical well equation to include it. With this theoretical development, it is now possible to confirm or monitor equalizer performance in terms of pressure drop from pressure transient analysis.
Introduction
With high oil prices prevailing, producers are more willing than ever to buy advanced wellbore equipment to improve well performance (Salamy et al. 2006; Lorentz et al. 2006; Williamson et al. 2000). Fig. 1 illustrates an equalizer production system, sometimes called an inflow control device (ICD). At sandface, fluids are forced to go through some kind of flow-restriction mechanism before entering the production tubing. Flow restriction is achieved by different means, such as spiral channels and narrow-gauge orifice to artificially generate extra frictional pressure drop at chosen downhole locations where early water or gas breakthrough may occur. Current equalizer production systems are built into the tubing or casing and cannot be adjusted or moved once installed. Because the exact well-completion interval (where early water or gas breakthrough occurs) cannot be predicted, most manufacturers recommend a uniform design (e.g., an equalizer device every 40 or 80 feet [ft]). The manufacturers claim a uniform design has a self-regulating function; whereby, high-producing zones are cut back automatically to allow a higher influx from low-producing zones. The self-regulating property comes from the rate-dependent skin characteristics of the ICD. The flow resistence provided by constrictions is exponentially proportional to the flow rate. However, the authors illustrate that equalizer placement can be optimized to have a more uniform production profile if the reservoir permeability along the wellbore can be quantified by means of an openhole flowmeter survey shortly after drilling. Gamma ray log, drillstem testing (DST) tests, and modular formation dynamics tester (MDT) tests also provide useful permeability data.
In general, equalizer application can result in a more uniform production profile, with better reservoir drainage for a very long horizontal well penetrating multiple isolated compartments.
Some field trials have shown that equalizer application can improve the well productivity index (PI). A twofold oil production rate increase had been reported (Al-Qudaihy et al. 2006). In theory, this observation does not reflect reality, because an equalizer introduces extra pressure losses, causing the total pressure drawdown for a given rate to be greater than before. The only reasonable explanation for improved PI is a formation damage cleaning effect (i.e., equalizer application promotes flow from low-production [damaged] zones) thus helping remove debris from drilling mud and completion fluids.
A typical smart-well application for multilateral wells is to control lateral flow rates by a downhole choke (Fig. 2). If water cut or gas/oil ratio (GOR) values exceed a preset value in any lateral, then the downhole choke is controlled remotely to cut down production in the affected lateral. For horizontal wells, we can group completion intervals into different sections. As in lateral control, the section ICV reduces production if a given section registers a high water cut or GOR value. If the well performance does not improve after several rate-reduction actions, the operator may shut down production completely for a given lateral or section if the economical limit, such as 95% water cut, is reached.
FDPSOs: The new reality, and a game-changing approach to field development and early production systems
