Do Complex Super-Gel Liquids Perform Better Than Simple Linear Liquids in Hole Cleaning With Coiled Tubing?

Abstract

The properties of the circulation fluid have a fundamental effect on solids transport. The shear stress at the solids bed and liquid interface, for a near horizontal wellbore, plays the key role in transport of the solids. The flow regime, geometric combination of hole/coiled tubing (CT) and eccentricity, also effect the rheological state of the liquid and have a significant impact on the solids transport efficiency. There is a need to differentiate between the superior solids suspension capabilities of the liquid and its hole cleaning efficiency produced when it is in motion. The most important concept is that, the greater the solids carrying capacity a fluid has, the more efficiently the hole can be cleaned.The challenge that presents itself is that once the solids fall and form a bed within the wellbore, how can the solids be re-entrained and transported out of the hole? In this paper, solids transport studies with several bio-polymers were conducted with a sophisticated flow loop. These studies highlight that these types of fluids bring some advantages and disadvantages. The carrying capacity and suspension properties of these fluids are superior but were hindered by other geometric influences on the velocity profile. Solids entrainment and re-entrainment into the fluid, as would be expected, is difficult to achieve without mechanical assistance.However, excellent efficiency of the fluid can be obtained and this paper presents some of the conditions under which this is practically achieved. Introduction For a typical fill cleaning process, the CT tags the top of the fill, and is run into the hole to a target depth while jetting into the solids (penetration stage). The hole is cleaned by; either circulating a clean fluid while keeping the CT stationary (circulation stage); or by pulling the CT out of the wellbore with continuous circulation (wiper trip stage); or by a combination of these stages. In past studies[1–4], several fluids have been used to conduct solids transport tests. Fluids previously examined are: water; 0.25% (by weight) Xanvis and 0.25% HEC gels. Based on these studies the following conclusions have been drawn. Horizontal Flow: The properties of the circulation fluid have an effect on solids transport. The shear stress at the bed interface for a near horizontal wellbore plays the key role in solids transport. Therefore, the flow regime, geometric combination of hole/CT and eccentricity also affect the rheological state of the liquid and have a significant impact on solids transport. Furthermore, there is a need to differentiate between the carrying capacity of the liquid and the hole cleaning effect produced by the flow. A consistent conclusion from the published references indicates that for a horizontal/near horizontal wellbore, hole cleaning is more efficient if a low viscosity fluid is pumped in a turbulent flow regime rather than a high viscosity fluid in a laminar regime. These previous studies are consistent with this trend and included a comparison of water, 0.25 % (by weight) HEC and 0.25% Xanvis polymers. The amount of solids that can be transported by a given volume of liquid is dependent on the rheological properties of the liquid. Xanvis and HEC polymer based fluids are more effective than water in terms of carrying capacity but unable to efficiently erode a stationary bed. (It is essential to keep in mind that CT is usually circulating the cleaning fluid at ‘low’ flow rates). In general, it is not possible to achieve in-situ velocities in a casing or open hole that are high enough to exceed the critical deposition velocity.

Sand Cleanouts With Coiled Tubing: Choice of Process, Tools and Fluids

“…Several cleanout techniques have been developed over the years, these include stationary circulation, wiper tripping (1,2,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) , reverse circulation (19)(20)(21)(22) , sand vacuuming technology (23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)36,37) , and venturi sand/junk bailers (4,22,(38)(39)(40) .…”

“…Wiper Trip Hole Cleaning (2,(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18) A comprehensive experimental test program conducted over the past 15 years (7)(8)(9)(10)(11)(12) has investigated solids transport for both stationary circulation and wiper trip cleanouts. The effect of multiphase flow, rate of penetration (ROP), deviation angle, circulation fluid properties, particle density and size, fluid rheology, pipe eccentricity, wiper trip speed, and nozzle type on solids transport was examined in detail.…”

“…In some cases, the sand can only be removed from highly deviated/horizontal large wellbores by the combination of using fluids with high solids-suspension property and the wiper-trip technology (1,11,16) . For pressure-depleted reservoirs (2) , nitrified fluids have to be circulated.…”

“…Special Fluids: Biopolymer and Foam (1,11,16,41) The most common fluids used in sand cleanouts include formation water, sea water, brine, and occasionally diesel or base oil, any of which can be co-mingled with nitrogen. However, in some cases, because of the wellbore completion size and low reservoir pressure, it is sometimes necessary to use fluids with improved solids suspension capabilities; these can either be water-based polymer systems with or without nitrogen or even foamed fluids.…”

“…Previously published studies (8,11) demonstrate that these types of gelled fluids bring some advantages and disadvantages. The carrying capacity and suspension properties of these fluids are superior but are hindered by other geometric influences on the velocity profile.…”