TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe major differences between conventional rotary drilling and Coiled Tubing drilling are the absence of pipe rotation and the continuous circulation of drilling fluids.• In rotary drilling the circulated fluid must be selected to support the cuttings while making a connection. In slide drilling, the circulated fluids can be continuously circulated. This capability greatly aids the use of gasified fluids in underbalanced drilling. • In slide drilling, the pipe does not rotate; while in rotary drilling, the pipe rotation enhances the cuttings transport by the agitation effect due to the pipe rotation and vibration. For a typical Coiled Tubing drilling job, the challenge is achieving the circulation rate required to keep the hole clean. Current field practice is to perform frequent wiper trips.The economics of hole cleaning are crucial to the industry and therefore we seek answers to questions such as:• What is the change in the cuttings bed height when the fluids flow rates are altered? • How long does it take to clean out an existing cuttings bed?• Is there a need to remove the cuttings bed fully before resuming drilling? In this study, 600 tests were conducted and a new computer program was developed for the prediction of cuttings transport in the multi-phase system (gas+liquid+cuttings). The sensitivity of cuttings bed height with respect to liquid/gas volume flow rate ratio, in-situ liquid velocity, ROP, inclination angle and circulation fluid properties was conducted. The hole cleaning time with both circulation mode and wiper trip is also discussed. The results from the sensitivity analysis presented in this paper indicate that: i) the fraction of the circulation liquid has a significant impact on the cuttings transport in underbalanced drilling with gasified fluids, ii) among different variables, the in-situ liquid velocity is the most important variable for cuttings transport, iii) the hole cleaning time decreases non-linearly with increasing fluid circulation rate.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis study was conducted to gain a more in-depth understanding of solids transport for coiled tubing workovers, cleanouts and drilling applications. Cuttings or particle transport in Coiled Tubing operations is a complex problem that is affected by numerous parameters. Predicting effective cuttings transport requires all of these parameters to be considered simultaneously. Tests were conducted to determine the effects of the following parameters: I) Different particle size, II)Fluid rheology, including water, gel, and multi-phase fluids, III)Pipe eccentricity, coiled tubing positioned on the low and high side of the wellbore.The effects of the different parameters were investigated in two different modes: the circulation mode, that involves the development of a cuttings bed or build-up of cuttings in the wellbore, and hole cleaning mode, which is cleaning out an existing cuttings bed. It will be shown that the results indicate: 1) for the tested particle size range (0.150 -7 mm), cleaning efficiency is partly dependant upon the particle's size, 2) with suitable agitation, a gelled fluid is more effective for cuttings transport than water in a highly deviated wellbore, 3) Pipe eccentricity has an effect on cuttings transport for different fluids and 4) for complete wellbore clean-up it requires many more hole volumes than previous 'rules of thumb' would indicate.

Summary In this study, 600 tests were conducted and a new computer program was developed for the prediction of cuttings transport in the multiphase system(gas+liquid+cuttings). The sensitivity of cuttings bed height with respect to liquid/gas volume flow rate ratio, in-situ liquid velocity, rate of penetration(ROP), inclination angle, and circulation fluid properties was conducted. The hole-cleaning time with both circulation mode and wiper trip is also discussed. The results from the sensitivity analysis presented in this paper indicate, first, that the fraction of the circulation liquid has a significant impact on the cuttings transport in underbalanced drilling with gasified fluids;second, that among different variables, the in-situ liquid velocity is the most important variable for cuttings transport; and, finally, the hole-cleaning time decreases nonlinearly with increasing fluid circulation rate. Introduction Cuttings transport has a major impact on the economics of the drilling process. Problems that may be caused by poor hole cleaning include stuck pipe, reduced weight on bit leading to reduced ROP, transient hole blockage leading to lost circulation conditions, excessive drill pipe wear, extra cost for special mud additives, and wasted time by wiper-trip maneuvers. Sand production is a common problem faced by many of the oil producers, especially in the heavy oil industry. Several cleanout options have been developed over the years, employing a number of different technical approaches. One of most common options is running in with coiled tubing and circulating the sand out with a liquid or gasified liquid. An important consideration in designing cleanout operations is the proper selection of the pump rate and circulation fluid. These parameters should be optimized in order to transport the sand to surface with the least cost. High circulation rates can cause higher costs and other operational problems. Over the past two decades, considerable effort has been expended into the research of cuttings transport in deviated wells with a single-phase flow. A large number of experiments have been conducted to study the effects of various parameters on cuttings-bed formation. A brief literature review was given by TUDRP.1–2 Experimental research on cuttings transport in inclined wells has been conducted using flow loops at the U. of Tulsa,3–6 the U. of Heriot-Watt,7 Mobil R&D Corp., M-I Drilling Fluid Co., BP Research Center, Inst. Francais du Petrole, and Petrobras.8–12 Several hole-cleaning correlations/models have been developed.4-6,13 Larsen,4 Jalukar,5 and Bassal6 conducted a total of 2,076 tests using the TUDRP's 5-in. and 8-in. flow loops. Based on the test results, they developed correlations to predict the critical velocity and cuttings-bed height. The correlations provide a means of analyzing cuttings transport as a function of operating conditions (flow rate, penetration rate, and rotation speed), mud properties (density, rheology), well configuration(angle, hole size, and pipe size), and cuttings size. Adari et. al.13 developed empirical models to correlate the cuttings-bed height and the hole-cleaning time to drilling fluid properties and flow rate for the wellbore near the horizontal position. Similar to the models developed in the mining industry,14–16 layer mechanistic models to predict the bed height and pressure drop. However, such models are not able to model cuttings transport at medium inclination angles (35-55°) due to the chaotic motion of the cuttings.1 Furthermore, there are various unknown parameters, such as friction coefficients and a turbulent diffusion coefficient, involved in the models. These coefficients have to be determined based on comprehensive test results. There is still a gap between the model development and field application.21 Most of the previous cuttings transport studies in the drilling industry mainly focused on finding the minimum critical velocity and bed height or total cuttings concentration in the wellbore annulus for conventional rotary drilling with mud fluids. Recently, Rodriguez22conducted solids-transport tests with gasified fluids in near-horizontal wellbores. Based on the concept of critical velocity, he developed correlations to predict the minimum air and water flow rates required in order to avoid the formation of a stationary solids bed. However, this concept still lacks information related to cuttings transport with two-phase fluids and the prediction of the hole-cleaning time. In fact, there are different transport mechanisms during the bed erosion (ROP=0) process and during cuttings transport while drilling (ROP>0).21 In this study, a comprehensive experimental test of cuttings transport with two-phase fluids was conducted. The effect of liquid/gas volume flow rate ratio, in-situ liquid velocity, ROP, inclination angle, and circulation fluid properties on cuttings transport was investigated. However, this paper's main focus is on angles close to horizontal. Based on the test results, a computer program was developed and the sensitivity analysis of cuttings transport parameters, such as cuttings-bed height and hole-cleaning time, was conducted. Experimental Setup The test apparatus (Fig. 1) was designed and constructed in accordance with the following requirements.Annular-flow steady-state conditions must prevail in every test case.The apparatus must allow the selection of the most important drilling variables (gas and liquid flow rates, well inclination, annular geometry configuration, cuttings concentration, and drill pipe size/eccentricity, etc.). The flow loop, shown in Fig. 1, was used throughout this project. The loop consists of a 20-ft transparent Lexan pipe with a 5-in. inner diameter simulating the openhole and a 2 3/8-in. steel inner pipe to simulate a drillpipe. The inner pipe is positioned on the bottom of Lexan pipe to simulate the worst case for the cuttings transport (eccentricity=100%).

Wiper trips are the current field practice to clean the hole for coiled tubing drilling or sand clean out operations. A wiper trip can be defined as the movement of the end of the coiled tubing in and out of the hole, a certain distance. In order to clean the solids out of the wellbore, a proper wiper trip speed should be selected based on the operational conditions. There is no previously published information related to the selection of the wiper trip speed. In this study, numerous laboratory tests were conducted to investigate wiper trip hole cleaning and how the hole cleaning efficiency is influenced by solids transport parameters such as;Nozzle Type,particle size,fluid type,deviation angle,multi-phase flow effect. The results indicate the following:Compared with stationary circulation hole cleaning, the use of the wiper trip produces a more efficient clean out.For a given operational condition, there is an optimum wiper trip speed at which the solids can be completely removed.Nozzles with a correctly selected jet arrangement yield a higher optimum wiper trip speed and provide a more efficient clean out.The hole cleaning efficiency is dependent on the deviation angle, fluid type, particle size, and nozzle type. Correlation's have been developed that predict the optimum wiper trip speed and the quantity of solids removed from and remaining in the wellbore for given operating conditions. The wiper trip provides an advantage for hole cleaning and can be modeled to provide efficient operations. Introduction Solids transport and wellbore cleanouts can be very effective using Coiled Tubing techniques, if one has the knowledge and understanding of how the various parameters interact with one another. Poor transport can have a negative effect on the wellbore whether it is for coiled tubing drilling or cleanouts, which may cause sand bridging and as a result getting the coiled tubing stuck. Coiled Tubing can be a very cost-effective technology when the overall process is well designed and executed. The highly deviated/horizontal well has placed a premium on having a reliable body of knowledge about solids transport in single and multi-phase conditions. In our previous studies1–2, a comprehensive experimental test of solids’ transport for the stationary circulation was conducted, which included the effect of liquid/gas volume flow rate ratio, ROP, deviation angle, circulation fluid properties, particle size, fluid rheology, and pipe eccentricity on solids transport. Based on the test results the data was analyzed, correlation's were developed, and a computer program was developed. In this study, the wiper trip hole cleaning effectiveness was investigated with various solids transport parameters such as, deviation angle, fluid type, particle size, and nozzle type. Based on these test results, an existing computer program was modified and adjusted to include these additional parameters and their effect on wiper trip hole cleaning. Experimental Setup The flow loop shown in Figure 1 was used for this project. It was developed in a previous study1–2. The flow loop has been designed to simulate a wellbore in full scale. This flow loop consists of a 20ft long transparent lexan pipe with a 5-inch inner diameter to simulate the open hole and a 1–1/2" inch steel inner pipe to simulate coiled tubing. The flowloop was modified and hydraulic rams were installed to enable movement of the tubing (see figure 2). The inner pipe can be positioned and moved in and out of the lexan to simulate a wiper trip. The loop is mounted on a rigid guide rail and can be inclined at any angle in the range of 0°–90° from vertical. When the coiled tubing is in the test section, circulating the sand into the test section and build an initial sand bed with an uniform height cross the whole test section. Then pull the coil out of the test section with a preset speed.

Control of capital expenditure on drilling/completion operations is important. In many instances the cost of drilling has meant that projects were deferred or cancelled completely. This paper discusses the factors which should be considered in reducing drilling/ completion costs by improving performance in the well pre-planning to well on production, cycle.Major technological advances in-equipment utilised in all aspects of drilling operations are also discussed, highlighting their benefits.