Underbalanced-Directional Drilling with Coiled Tubing - Challenges and Solutions

Abstract

The inherent advantages and limitations of drilling with coiled tubing have been the subject of many presentations in the last several years. The potential benefits that coiled tubing drilling systems offer have prompted development of several competing systems that are now being brought to the market. Although each of these approaches share some similarities, unique features have been introduced that enhance the value of the available systems. Full exploitation of coiled tubing drilling systems dictate that a practical approach be taken. Specifically, the most attractive approach is the one most highly leveraged to deriving the benefits offered by using coiled tubing. Because the coiled tubing drilling system is subject to limitations with respect to force delivery and the inability to rotate, the application of this emerging technology needs to be directed to a niche where it provides the operator best value. Coincident with the developments in coiled tubing drilling, industry's acceptance of underbalanced drilling techniques has been growing. It is now widely understood that the advantages of coiled tubing drilling are most evident in underbalanced operations. These advantages of technology will be applied to a wide range of well-finishing and reentry operations to increase both the productivity and recovery of hydrocarbons from existing fields. This paper presents the latest technology being applied in underbalanced coiled tubing drilling operations and highlights the additional advantages of using a pressure deployment system. Operations conducted in the first ten months of 1996 using these tools are reviewed. Introduction Over the last few years, the significant growth of underbalanced drilling in horizontal wells in Western Canada has created a significant opportunity for the use of coiled tubing. Development of directional drilling assemblies for coiled tubing has now opened up the market for coiled tubing drilling systems to be used for the drilling of horizontal wells while underbalanced. Coiled tubing drilling market segments in Canada have focused on niche applications. The specific market has been underbalanced drilling through the reservoir. The reason coil has been chosen to focus in on this particular market is coil's proven record of successfully operating in a live well environment and the operational and technical advantages coil offers while functioning in this these conditions. Coiled tubing is an excellent candidate for drilling if the well is to be drilled underbalanced. This is especially significant when drilling sour gas wells. The scope of this discussion will be focused on the Western Canadian market where coil is being used for underbalanced drilling. The paper will review the latest technology being used in coiled tubing directional drilling applications. Challenges that are inherent with this emerging technology and the unique solutions which have been employed to address and overcome these challenges will be discussed. In addition, a brief overview of the horizontal drilling jobs performed to date will be discussed. Underbalanced Drilling Underbalanced drilling (UBD) is generally considered to involve two phase fluid circulation (nitrified fluid) during drilling to lower the bottom hole pressure to below the reservoir pressure. UBD has become a widely recognized and viable alternative technique to conventional overbalanced drilling, which is especially advantageous in horizontal well drilling due to the increased time of formation exposure.

Numerical Modelling of Cuttings Transport with Foam in Inclined Wells

“…Apart from having a good lifting ability and the ability to maintain an underbalanced drilling condition, foam is also used to remove formation fluids that enter the borehole while drilling and also serve as an insulating medium if loss circulation is a problem. Applications of foam as a drilling fluid in many drilling operations, and the results from various field cases are well documented [13][14][15][16][17][18][19][20][21][22][23][24]. port, the fluid velocity at the bottom should be at least 10% higher than the terminal velocity at the same depth.…”

Numerical Modelling of Cuttings Transport with Foam in Inclined Wells

“…Apart from having a good lifting ability and the ability to maintain an underbalanced drilling condition, foam is also used to remove formation fluids that enter the borehole while drilling and also serve as an insulating medium if loss circulation is a problem. Applications of foam as a drilling fluid in many drilling operations, and the results from various field cases are well documented [13][14][15][16][17][18][19][20][21][22][23][24]. port, the fluid velocity at the bottom should be at least 10% higher than the terminal velocity at the same depth.…”

A Comparative Study of Hydraulic Models for Foam Drilling

“…Foam has been used as a drilling fluid in many drilling operations, and the results from various field cases are well documented in the literature (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) . In many cases, drilling with foam has been shown to provide significant benefits, including increased productivity (by reducing formation damage), an increased drilling rate, reduced operational difficulties associated with drilling in low pressure reservoirs (e.g., lost-circulation and differentially stuck pipe), and improved formation evaluation while drilling.…”

“….................................................................. (21). Consequently, they have defined the volume-equalized Fanning friction factor as follows:................................................................(22) By using the principle of mechanical energy balance, they derived the following equation to determine frictional pressure losses during the isothermal, steady state flow of compressible fluids in horizontal pipes: ........................................................................................................................(24) ................................................................(25) ...................................................................................(26) ................................................................................... (27).…”