Sand production is a common problem with unconsolidated formations. It is very challenging to successfully remove formation sands with conventional methods in a large deviated wellbore with a low pressure gradient formation 1. Since 1995, a technology combining concentric coiled tubing (CCT) with a jet pump has been developed and used to remove both the drilling fluids and solids. Initially it was developed for horizontal heavy oil reservoirs where pressures are low and viscosity is high, without placing hydrostatic loads on the reservoir. The job data from more than 600 sand/well vacuuming operations worldwide has been compiled into a database. This paper reviews the well information and the key operating parameters: maximum depth, bottom hole pressure gradient and pump rate. The engineering challenges, best practices and lessons learned for the sand/well vacuuming process are also summarized. Analysis of this data yields a better understanding about this vacuuming technology and provides good guideline for future practice. Case histories are provided which demonstrate how to deploy the different sand/well vacuuming bottom hole assemblies (BHA), to; increase the penetration capacity with a jetting tool; entering multi-laterals with an entry guidance system; accessing small size holes with a micro-vacuuming tool; and to achieve extended reach under extreme conditions. Post job analysis indicates CCT vacuuming technology reduces the skin damage and increases the production compared to non-vacuumed wells. Moreover, the details from sand and other fluid influx profiles obtained along the wellbore based on the analysis of the returns during the vacuuming process, could be used to evaluate well production and assist in formulating a management strategy. Introduction During the drilling of most horizontal heavy oil wells, the drilling fluid's hydrostatic column produces fluid losses to the formation due to the low bottom hole pressure (BHP). Otherwise, the presence of a filter cake adhered creates an artificial layer between the formation face and the outer part of the slotted liner, affecting the pressure transference from the reservoir, in other words, creating an additional pressure drop from the formation to the wellbore. After the drilling operation is completed, the production pump is run in the hole and is used to retrieve the drilling fluids and the filter cake remaining in the well. The problem with this method is that the suction produced by the production pump is mainly in the nearest zones to the pump and does not create significant suction in the toe of the horizontal section. Therefore, the well will produce predominantly from the heel and have less production from the toe. Sand production is also a common problem faced by many of the heavy oil producers worldwide. A slotted liner acts as a partial barrier, grading effects at the slots often still result in sand migration into the wellbore and, hence, a lower production rate. The low production flow rates contribute to increased deposition of the sand in the highly deviated wellbore. Several cleanout options have been developed over the decades, employing a number of different techniques and approaches 1. However, coiled tubing (CT) or conventional jointed pipe often incorporate the need for high circulation rates, special fluids or reverse circulation methods to remove the solids. With high rates and high specific gravity water based fluids, conventional sand cleanout methods often apply an excess pressure on the formation and this results in lost circulation returns to the low formation pressure reservoirs. A typical reservoir pressure in these wells may be as low as 0.04 psi/ft. This makes sand removal virtually impossible and creating damage to the formation likely. Nitrogen can be used to reduce hydrostatic pressure, but this necessitates a very specific job design and execution and can require large quantities of liquid nitrogen in the case of horizontal wells located in some remote area.

The use of Coiled Tubing in the workover and drilling sectors of the industry has seen considerable growth. This is due, in no small part, to the changes in tubing manufacturing techniques that have led to better materials and more consistent tubing performance. Consistency of tubing performance has enabled a large body of research work to be conducted in order to understand the low cycle fatigue and mechanical behaviour of coiled tubing in service. When Coiled Tubing (CT) is used in oilfield applications it is subject to numerous plastic bending reversals which impose low cycle fatigue damage on the tubing. This damage is cumulative and leads to eventual failure - loss of pressure integrity and in some cases catastrophic failure. With the research work undertaken over the last several years the boundaries of the operating envelope have been better identified and can be predicted with the use of fatigue management computer models. A result of this knowledge is that, as fatigue failure can be predicted for a given tubing and tubing material, other factors are becoming influential in some of the premature failures experienced in field operations. These factors are often found to be such things as manufacturing flaws, corrosion and mechanical damage. To further enhance the reliability of CT in service it would be beneficial to detect such flaws before the tubing is run into a well when the cost of tubing failure can be expensive. Several non-destructive inspection (NDT) devices are becoming available on the market, each with their advantages and disadvantages. This paper summarises experience gained in the Canadian Oilfield by application of current NDT technology over the last 24 months and what alterations have been made to operating procedures as a result.

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.

This paper was prepared for presentation at the 1998 SPE/ICoTA Coiled Tubing Roundtable held in Houston, Texas, 15-16 April 1998.

Carbon steel coiled-tubing (CT) strings have been used in sour wellbore environments for many years. The use of CT in sour service has increased by job number, job complexity, pipe size, and the stresses to which the pipe is subjected. A number of papers have been written on the steel chemistry and low-cycle fatigue behavior. These papers have been based on both theoretical and laboratory work. Great progress has been made in understanding the chemical and physical interaction of CT and H 2 S, but little information is available from "real-world" situations in which the pipe has been worked in a variety of job types (e.g., acidizing, gas lifting, and drilling) and in which a large number of other factors may come into play (e.g., injector damage, well-stimulation chemicals, sour inhibitor application techniques, erosion of inhibitors, CO 2 , and high-chloride water production).This paper discusses the application of a CT technical specification (based on theoretical and laboratory work) in the operational world. Comparisons will be made between theoretical expectation and practical observation for 70-and 80-grade CTs with regard to low-cycle fatigue, pipe life, and damage in sour environments.