Analysis of Drilling Fluid Circulating Pressure Loss in Hole Annulus for Microhole Drilling
The microhole drilling (MHD) technology is one of cutting-edge drilling technologies with wellbore diameter less than 88.9 mm and taking coiled tubing (CT) as drilling string to deliver the bottomhole assembly to drill ahead. The normal circulation of drilling fluid is affected because of huge annulus drilling fluid circulating pressure loss (ADFCPL) caused by small diameter wellbore, narrow hole annulus and deep well. For three flow regimes of power-law fluid in MHD, the computing models of ADFCPL are built by analyzing the relationships among annulus drilling fluid parameters according to power law fluid flow state equation. The ADFCPL with different flow rate, CT diameter, well depth, eccen- tricity and so on is calculated for the hole annulus of MHD. The calculation results show that: in 89mm diameter MHD, the ADFCPL is huge. It increases with the increase of outer diameter of CT and average flow rate of drilling fluid, and in- creases linearly with the increase of well depth, and decreases with the increase of eccentricity. The bigger the hole annu- lus is, and the lower the flow rate is, the less the impact of eccentricity acts on the ADFCPL is. Thus, the ADFCPL can be reduced by decreasing the outer diameter of CT and the average flow rate of drilling fluid in hole annulus. Only low flow rate can be used to drill deep well. The research results may be useful for MHD parameter selections related to the ADFCPL.
Experimental Investigation of Frictional Pressure Losses in Coiled Tubing
This paper presents an experimental investigation of tubular frictional pressure loss in coiled tubing and straight sections of seamed and seamless tubing. Fluids investigated include water, linear guar gum and hydroxypropyl guar (HPG), and borate-crosslinked guar gum and hydroxypropyl guar, under conditions typically encountered in many coiled tubing field applications. The equipment used includes a system of one 1000 ft and two 2000 ft coiled tubing reels that can be arranged to provide total coiled tubing lengths of 1000, 2000, 3000, 4000, and 5000 ft. The system also includes straight sections of seamed and seamless tubing with the same nominal diameter (1 1/2 in.) and wall thickness (0.156 in.) as that of the coiled tubing. The investigation focuses mainly on the effects of coiled tubing curvature, tubing seam, fluid pH and shear history on frictional pressure loss. Results obtained with water indicate that curvature as well as the seam inside the coiled tubing significantly affect the frictional pressure losses. Results obtained with various polymer solutions and gels, however, suggest that tubing curvature has a more significant effect on the frictional pressure losses than the tubing seam. Moreover, it is observed that for borate-crosslinked HPG the pressure gradient is dependent on both the fluid pH and the length of coiled tubing across which it is measured. However, for borate-crosslinked guar gum the pressure gradient is a function of pH and is not very sensitive to the length of tubing along which it is measured.
Jet Drilling Tool: Cost-Effective Lateral Drilling Technology for Enhanced Oil Recovery
The paper describes a new coiled tubing conveyed drilling technique, were several new well bores are jet-drilled perpendicular from the mother well and into the reservoir formation. This technology is targeted for Enhanced Oil Recovery (EOR) in both existing and new field developments. The objective is to improve the production profile around the mother well, by penetrating the damaged skin zone, and connecting to possible hydrocarbon pockets left behind in the reservoir. The Bottom Hole Assembly (BRA) is configured to jetdrill several slim laterals, all in one coiled tubing (CT) run. This through tubing operation has the potential to create up to ten, 50 m long, and 1-2 in. diameter laterals at the exact desired depth in the mother well. The BHA consists of two main parts; a casing drilling machine and a high-pressure hose and jet-nozzle. The hose is spooled from the BRA as the lateral is drilled into the formation. The main issues presented in the paper are: 1. The new jet tool functional characteristics 2. The theoretical aspects of jet drilling; penetration mechanisms and self-induced nozzle pull force 3. Laboratory experiments (confirmation of theoretical models) 4. The jet drilling effect on improved well production (production simulations). The technology is an attractive substitute or supplement to acid and proppant fracturing, perforating services and conventional sidetrack drilling. Introduction An important issue when stimulating a producing or injection well is to control the exact placement and direction of the treatment. This may represent a challenge in conventional fracturing and acid stimulation methods. Stimulating low productivity zones exposed together with good productivity zones represent in many situations a problem, since the treatment is improperly diverted into the low productivity zones. The stimulation fluid tends to flow into the good zones, which in many cases were not the target for the stimulation. Furthermore, fractures may open pathways along the casing wall, causing zonal isolation problems in the well. A variety of diversion techniques have been developed in the industry today, in order to achieve improved stimulation control. The success of these techniques varies. This paper describes a technology that provides means for improved control of the EOR treatment. The technology provides real time signals, which acquires exact measurements of tool depth and direction. No pre-treatment activities, like pulling tubing (dependent on size), section milling and/or under-reaming is required prior to the jetting operation. The tool will be a valuable supplement or substitute to conventional services like: Perforating Matrix Acidizing Fracturing Conventional sidetrack, slim hole drilling. The Jetting Technology Development Project — Definitions and Functional Descriptions The tool is a coiled tubing conveyed electrical bottom hole assembly, designed and developed to create a number of laterals perpendicular to the mother well in one CT run. The laterals remain barefoot and are created by means of the jetimpact generated when pumping fluid at high pressure through the nozzle-head. The energy created when the fluid exits the nozzle-head is also providing the required forward force to pull the high-pressure hose into the lateral. The main design criteria for the development were: 1. Provide 4-10 laterals radially from the mother-well, each 1-2 in diameter and up to 50 meters long 2. The entire treatment performed in one CT run 3. Temperature and pressure rating; 120°C and 690 bar 4. Function in both live and dead wells DISCLAIMER: This report addresses a like process developing methodologies utilized in Lander’s LJD theories and applications. Society of Petroleum Engineers 2 P. BUSET, M. RIIBER, A. EEK SPE 68504 5. Function in sour environment 6. The data acquisition system should provide real time indication of tool position and lateral exit direction, as well as positive indication on operating system effectiveness 7. The tool shall be designed for operation in 4 1⁄2” or larger inner diameter (ID) completions. The main features of the Jet Tool are the ability to create a hole in the casing and to subsequently jet a lateral into the formation through the casing exit hole. To achieve this a Drilling Machine and a Jet Drum has been developed. The Drilling Machine contains a drill bit driven by a combination of an electrical motor and a hydraulic piston, creating a 1 1⁄2” diameter hole in the casing. The Jet Drum holds a 3/8 in, 50 m long jet hose, which is coiled around a cylindrical drum. The drum has an electric motor enabling the drum to feed the hose out while creating the lateral, and to spool the hose back in. The Drilling Machine and the Jet Drum are the main components of the BHA. In addition it contains the following components (see fig 1): Tubing End Connector Controller Unit/Power Pack Anchor Orienter/Indexer Steering-tool Stroke Cylinder. The BHA is run on a CT with an internal electric line for power supply and communication to/from the surface, and a 1⁄2 in. outer diameter (OD) capillary line for jet fluid supply. The Controller Unit is the brain of the tool and it activates the various tool functions according to the signals from the tool operator at surface. The controller includes an internal hydraulic power-unit and a solenoid valve operated distribution system. A hydraulically operated anchor has been developed and incorporated in the BHA. Its function is to attach the BHA to the casing wall in order to maintain it in exactly the same position from the point that the casing hole is being drilled until the lateral has been jetted. One of the main objectives with the treatment is to enhance the production pressure distribution and to determine the depth and direction of the lateral. The hydraulically operated orienter in the BHA, enables the tool to create laterals in various directions perpendicular to the mother well. The Orienter rotates the lower part of the Jet Tool (below the anchor) and positions the tool face in the requested direction. Verification of direction comes from a steering tool located below the orienter. A Stroke Cylinder is placed above the Drilling Machine and Jet Drum. Its function is to position the Nozzle Head exit in front of the casing hole created by the Drilling Machine. The Stroke Cylinder is hydraulically driven. Tool Operation: 1. Lower the BHA down to the reservoir target depth 2. Attach the tool to the casing wall by means of the anchor 3. Drill a hole in the casing/production liner with the drilling machine 4. Stroke out the telescopic joint to position the nozzle head exit in front of the hole in the casing 5. Jet a lateral into the formation by pumping the jetting fluid through the internal capillary tube, into the high-pressure hose, and finally through the jet nozzle 6. Retract the telescopic joint 7. Reposition the tool, either by vertical repositioning, or by rotating the tool face by means of the orienter 8. Repeat the procedure, and pull out. The Jetting Tool Prototype has been developed over an 18 months period. The Drilling Machine and the Jet Drum have been manufactured and tested in accordance to the functional requirements. The Drilling Machine proved to drill through a 5-1⁄2 in., 17 lb/ft, Cr 13 casing in 9 minutes. The Jet Drum has been function tested by running the jet hose in and out from the jet-drum with the hose pressurized up to 220 bar. Study of the Penetration Mechanism set in force by the Jet Nozzle effect Penetrating hydrocarbon formations with water-jet energy is by no means a new invention. The jet power effect has been employed for various down hole applications. Veenhuizen (1) and Kolle (2) describe the effect of applying jet energy in combination with conventional drill bit technology in order to enhance the rate of penetration in hard formations. Dickinson (3), Maurer (4) and Pols (5) describe jet penetration technologies where laterals are created purely by use of clean water jet energy. The jet penetrating efficiency in different rocks along with various nozzle configurations and operating jet parameters have been frequently discussed topics. This data has been incorporated in this study during the development process. The paper focuses on the observations related to the specific nozzle head as illustrated in fig 2 and how the jet power generated through this nozzle head acts on the formation. Both the various penetrating mechanisms and the nozzle heads self-generating net forward pull force are discussed. Penetration Effect. Four main penetration mechanisms were identified: Surface Erosion Hydraulic Fracturing Poroelastic tensile failure Cavitation. Surface erosion. Surface erosion is the process where rock fragments are removed from the surface of the rock due to the shear and compression forces exerted on the rock surface due to the jetting flow. It is reasonable to assume that this process takes place, but the effectiveness is yet to be defined. There is in principle no difference between this process and the process taking place in conventional drilling, thus the energy required should be more or less equal. The impressive penetration rates SPE 68504 JET DRILLING TOOL: COST-EFFECTIVE LATERAL DRILLING TECHNOLOGY FOR ENHANCED OIL RECOVERY 3 reported from tests indicate therefore that more effective processes also take place. Hydraulic fracturing. As the build-up of pressure at the stagnation point diffuses into the formation, the formation may fail in tension if this pressure is higher than the stresses set up by the far-field formation stresses. Figure 3 shows a sketch of this mechanism. This pressure diffusion will take place as long as the permeability is not negligible. However, the characteristic size of the volume with elevated pore pressure will be the same as the characteristic size of the area hit by the water jet. As the water jets are fine, such hydraulic fractures will not extend far into 