Near Wellbore Cleanup in Openhole Horizontal Sand Control Completions: Laboratory Experiments

Abstract

Wellbore cleanup in horizontal, open hole sand control completions has been the subject of many publications in recent years. Although a large majority of horizontal wells have been standalone screen completions, an increasing number of these wells are being gravel-packed, particularly in deep water, sub sea environment where reliability of the sand face completion is of utmost importance due to prohibitively high cost of intervention. In such wells, increased significance of "doing it right the first time" further necessitates an emphasized consideration of wellbore displacement and filter cake removal treatments. Although a substantial amount of laboratory data on filter cake cleanup are available in the literature, a great majority of these data are relevant to non-gravel-pack completions. In field practice to date, cake cleanup in GP completions has almost exclusively been done after gravel packing and typically involved coiled tubing. Although several new methods have recently been proposed and successfully practiced in several applications (e.g., inclusion of cake-breaking chemicals into gravel-pack carrier fluids, post-GP breaker treatments immediately after GP w/o requiring coiled tubing), laboratory data directly applicable to such conditions have been scarce. In this paper, we present laboratory data relevant to gravel-packed completions. We show that the cake removal time scales in the presence of a gravel-pack are longer compared to absence of a gravel-pack on top of the filter cake. The degree of delay is shown to depend primarily on carrier fluid viscosity and whether the breakers are included in the carrier fluid or introduced as a post-GP treatment. It is further shown that including breakers in brine during water packing must be exercised with extreme caution since even slow-reacting breakers can yield premature screen out due to increased losses should external cake erosion occur. Introduction A large fraction of wells drilled in reservoirs requiring sand-control are being completed as horizontal open holes. Although a large fraction of these wells have been completed with screens-only, an increasingly higher number of these wells are being gravel packed, particularly in deep water and sub-sea completion environment where reliability of the sand face completion is of utmost importance due to prohibitively high cost of intervention. Furthermore, because the costs associated with filter cake cleanup treatments are typically marginal compared to potential intervention costs, a thorough cleanup treatment is considered an integral part of the completion in such wells, in order to maximize well productivity and longevity, and provide more uniform production profile and avoid premature water or gas breakthrough, although the actual cleanup methodology, including the type of chemicals and the placement techniques may vary significantly. Cake cleanup in gravel pack completions has traditionally been done after gravel packing, and typically with coiled tubing.1 Several new techniques have recently been proposed.2,3 These involve incorporating breakers into the gravel-pack carrier fluid to place the cake-breaking chemicals into the wellbore during gravel packing, as well as a modified service tool that can be used to displace wellbore fluids and spot breaker solutions by allowing circulation down through the wash pipe and up through the wash-pipe/base-pipe annulus.2

Open-Hole Horizontal Drilling and Gravel-Packing With Oil-Based Fluids - An Industry Milestone

“…Although this breaker system gave equivalent results to those obtained with oil-based RDF systems that will be discussed shortly, it induced complete losses after ~ 6 hours, which introduces high risk of complete losses while water-packing and thus a premature screen-out yielding incomplete packing, particularly considering the additional risk of cake erosion and thus significantly lower time period for inducing high losses as discussed in the literature. 16 An alternative approach would be to use a circulation tool that would allow spotting of the same CAS/Enzyme cake cleanup treatment immediately after waterpacking. 17 However, this approach was eliminated once the decision to gravel pack with the alternate path technique has been made due to much higher success ratio compared to water-packs.…”

Design Methodology for Selection of Horizontal Open-Hole Sand Control Completions Supported by Field Case Histories

“…It has been demonstrated, through laboratory experiments, that cake removal during gravel packing with water is a risk that is not worth taking if a modified work string that allows circulation immediately after gravel packing is used. 31 Recent work by Brady et al 32 has shown that gravel packed wells require an enzyme or an oxidiser treatment as a minimum depending on the mineralogy (clays, clean sand etc.) along the horizontal well and gravel size, as also shown by Hodge and Burton.…”

Laboratory Development of a Novel, Synthetic Oil-Based Reservoir Drilling and Gravel-Pack Fluid System That Allows Simultaneous Gravel-Packing and Cake-Cleanup in Open-Hole Completions

“…Subsequently, a filtercake was formed on the core at 300-psi overbalance at either 170 or 200 o F over a 16-hour time period, with the reversible S/OB-RDF using a modified HPHT static fluid loss cell. 5 After 16-hours of filtration, the excess RDF was poured out of the cell. Then, a gravel slurry with the S/OB carrier fluid incorporating a pH-modifier/CaCO 3 -dissolver (CAS) was placed on top of the filtercake, with some excess carrier fluid left above the gravel pack to simulate the fluid left in the base pipe at the end of gravel-packing.…”

“…This is consistent with the results reported by Brady et al for water-based-RDF filtercakes. 5 In order to investigate the effect of temperature on breakthrough kinetics, two tests were run at identical conditions, one at 170 and the other at 200 o F. As seen in Figure 4, the breakthrough time of ~ 90 minutes at 200 o F is about a factor of 3 shorter than that at 170 o F. Depending on the length of the interval to be gravel-packed, CAS systems with higher pH may be needed at elevated temperatures.…”