An Openhole Memory-Logging System for High-Angle Wells and Bad Hole Condition.
- P.A.S. Elkington (Reeves Oilfield Services) | M.C. Spencer (Reeves Oilfield Services) | D.L. Spratt (Reeves Wireline Services)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- February 2004
- Document Type
- Journal Paper
- 33 - 39
- 2004. Society of Petroleum Engineers
- 1.2.7 Geosteering / reservoir navigation, 1.6.1 Drilling Operation Management, 5.8.7 Carbonate Reservoir, 5.7 Reserves Evaluation, 1.6 Drilling Operations, 5.3.4 Integration of geomechanics in models, 1.12.1 Measurement While Drilling, 4.3.4 Scale, 1.11 Drilling Fluids and Materials, 2.4.3 Sand/Solids Control, 1.7.5 Well Control, 1.10 Drilling Equipment, 1.12.2 Logging While Drilling, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.6.1 Open hole/cased hole log analysis
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A mechanism for conveying logging tools inside drillpipe has been developed that reduces the risk and cost of acquiring openhole formation evaluation data in high-angle wells and bad hole conditions. The measurement string is housed inside drillpipe, where it is protected while running in, and pumped into open hole close to final depth. Wireline tools are used for data-quality reasons, but the wireline has been eliminated, giving time, access, and well-control advantages relative to wireline pipe-conveyed logging (PCL). It is an alternative to the formation evaluation element of logging while drilling (FE-LWD), where steering decisions do not rely on real-time petrophysical analysis, particularly when the risk to the bottomhole assembly (BHA) is high. The system's ability to acquire data while conditioning the hole contributes to its efficiency and is advantageous in bad hole conditions.
A 1.4-km horizontal test loop was constructed to help develop and prove the tool deployment and signaling mechanism. Insights gained during this process resulted in the development of novel payload delivery seals - key components in the system.
Formation evaluation data have been acquired in 220 wells; they include horizontal wells for which other logging solutions are unattractive for reasons of accessibility and/or cost. Knowledge gained from the interpretation of these data sets has influenced completions in some wellbores and guided remedial action in others.
Openhole formation evaluation logs are acquired with FE-LWD tools during (or soon after) drilling and/or with wireline tools after the drillstring has been pulled from the hole. FE-LWD is preferred if it reduces the number of trips in the hole in which associated rig costs are high, and it is selected when real-time formation evaluation is needed to guide the drilling process. Wireline logging, on the other hand, is a more mature technology with a broader range of developed measurements and is generally the more cost-effective option outside high rig-rate environments.1
Basic logs (such as navigation and gamma ray) are acquired from surface to total depth (TD) in many directional wells. Density, neutron porosity, velocity, and other FE-LWD logs are generally run over smaller intervals.
Wireline tools rely on gravity to get to TD in low-angle wells, but in high-angle, horizontal, and extended-reach wells, they are pushed to the bottom on drillpipe in wireline PCL. They are occasionally conveyed on coiled tubing with an integral wireline. FE-LWD is the more elegant solution in high-angle wells, but its reliability (particularly in bad hole conditions) and its high lost-in-hole charges are disadvantages.
Many horizontal wells (particularly in land locations) are logged with no more than basic LWD. In the western Canada sedimentary basin, for example, fewer than 10% of horizontal wells return porosity/resistivity/acoustic data because of the high cost and/or risk associated with conventional acquisition. Bit-size and bend-radius restrictions are additional constraints.
It was against this background that a hybrid system - the well shuttle - was developed. It combines aspects of the LWD and wireline methods but seeks to mitigate some of the weaknesses of each. In particular, the measurements are of the type and quality associated with wireline tools, but they are conveyed to the logging interval inside drillpipe rather than outside, thus avoiding exposure to potentially catastrophic loads. Data are acquired after drilling, but the tools are not exposed to the well for extended periods, giving a reliability advantage relative to FE-LWD.
Description of the System
The shuttle comprises the logging tools, drillpipe, and mechanisms for retaining and releasing the tools (Fig. 1). A rasp joint and an open-ended reamer bit can be included to aid re-entry and to assist conditioning of the well.
The logging string is housed inside drillpipe at the surface and remains inside until tripped to TD; there is no wireline. A dart pumped from the surface causes the tools to move into open hole while being retained by a collar in the BHA. Data are acquired while tripping out.
Three shuttle sizes have been developed: 6 1/2-in. outside diameter (OD) for wells with a minimum 8 1/2-in. bit size, a 4 3/4-in. OD for wells with a 6-in. minimum bit size, and a 3 1/2-in. OD variant for wells as small as 4 1/4-in. bit size.
The openhole string comprises compact format tools with an OD of 2 1/4 in. - small enough to be conveyed inside the slimmest shuttle variant. 2 They were developed initially to replace previous-generation tools for wireline operations and are qualified for hole sizes up to 12 1/4 in. (16 in., in the case of resistivity measurements). Measurement performance was monitored in 7,000 wells over a 4-year period before battery and memory modules were added for wireless conveyance. The availability of a proven measurement technology at the appropriate size was a key factor in the decision to develop the new conveyance system.
The primary measurements are array induction, dual laterolog, shallow high-resolution resistivity, formation density with photoelectric (Pe) and caliper curves, natural gamma ray, neutron porosity, and acoustic slowness (inverse velocity). Ancillary measurements include two-arm caliper, navigation, and temperature. A repeat formation-pressure tester currently available in wireline mode is being developed for wireless operations. Dipole sonic (to determine shear velocities) and a resistivity imaging tool are under development. Tools are rated for continuous operation to 257°F and 12.5 kpsi.
In wireless mode, batteries provide the power. Battery life is assessed for each job on the basis of the tool string configuration and predicted borehole temperature (battery life increases with temperature up to approximately 250°F). A single module powers a triple combo (induction, gamma, Pe density and neutron porosity) for 19.3 hours at 140°F - sufficient for most operations. Extended-life battery packs are used for operations of long duration or for more-complex tool strings. Second-generation battery packs (that restrict power consumption while running in) substantially increase the downhole operating time and satisfy the additional power requirements of planned future tools.
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