A New Methodology to Safely Produce Sand Controlled Wells With Increasing Skin

Abstract

Monitoring Deep Water Gulf of Mexico (DW GoM) wells with gravel-pack and frac-pack completions is an increasingly challenging task. Wells often experience increasing skin, adding to the risk of completion failure. Historically, sand control completions have experienced a 15% rate of sand related completion failures (King 2003). The industry tends to qualitatively evaluate safe target rates as skin increases. Reducing the flow rate based entirely on an increase in global skin can be too conservative and over-restrict target rate. Thus, it is important to know which components of the increase in skin can cause the completion to fail. Furthermore, it is not well understood how to quantify a safe target rate with the increased skin. This paper will present a new methodology to evaluate the components of skin increase which could cause sand control completions to fail. The failure mechanism we are addressing is perforations plugging by movement of fines and sand. Our new methodology helps quantify the risk and convert it into a safe target rate. This paper will also present case studies of oil and gas wells in the Na Kika Asset, in DW GoM where this methodology was successfully applied. The well completions are monitored with BP's flux based approach, (Tiffin 2003; Stein, Chitale, et al. 2005; Keck, et al. 2005). In all cases, the wells experienced increased skin, causing the engineers to choke back the well. The analysis showed that some of the skin increase was due to multiphase effects as the reservoir pressure was below the saturation pressure. Accounting for multiphase flow effects resulted in a 30% higher safe operating rate limit than with a conventional analysis. We also determined which skin components likely caused perforations plugging, thereby increasing the completion flux. The results allowed the Na Kika Asset to produce these wells at their maximum allowable safe operating rate with the higher skin, while producing within the BP's flux based guidelines. Introduction Setting a safe target rate for gravel packed DW GoM wells is a complex task of maximizing production while preserving the completion integrity. An industry study done by King (2003) showed a 15% failure rate in gravel packed completions. Operators control these wells using a maximum drawdown limit and generally over-constrain the production to avoid failures. Gravel packed and frac-packed wells have a tendency to build skin in and around the completion. It is believed that skin increase can cause completion damage. Before this study BP and the industry used a qualitative approach in determining the reduction in production necessary to mitigate the increased risk of well failure. Skin can increase due to various reasons such as fines migration, pseudo-skin due to relative permeability effects etc. Some of these skin components can be responsible for plugging the perforations and/or screens increasing the risk of failure and need to be accounted for in determining a safe target rate. We believe that some of the other skin components may not increase completion damage risk and can be discounted allowing favorable rate determination. To address this issue, BP set out to develop a quantitative relationship between failures and skin increase to improve upon the previously published flux based approach (Tiffin 2003). This work will present how the relevant components of skin can be used to correct the flux calculation.

An Automated Software Workflow To Optimize Gulf of Mexico Lower Tertiary Wilcox Sand Reservoirs

“…It is also important to note the large differences in the gravel pack and perforation tunnel skin in the Lower Tertiary completions vs. conventional high permeability GOM wells. Although certain sources show that high skin from gravel and perforation induced effects may mask the fracture (Welling 1998;Chitale et al 2009), the maximum skin factor on any rate was less than 0.1, even with gravel pack tunnel permeabilities of less than 10 Darcy and effective perforation of 2.625 (see Table 7). The low flow rate per perforation at the casing (low casing velocity) and low permeabilities of the reservoirs indicate that fracture effects will dominate the skin response for these types of wells.…”

A Well Flux Surveillance and Ramp-Up Method for Openhole Stand-Alone Screen Completion

“…They are non-surveillance models because there is no direct linkage of surveillance results to update flux calculations. Simple surveillance models use pressure transient analysis (PTA) results and completion information to evaluate the changing well performance and adjust the ramp-up (Wong et al, 2003) and long-term surveillance operations (Chitale et al, 2009). The complex surveillance model evaluates well performance and adjusts well operations using probabilistic completion failure risks and coupled reservoir and completion simulations (Cameron et al, 2018).…”