Introduction
This article discusses the application of two wellbore pressure-containment
integrity (WPCI) treatments that substantially increased the
pressure-containment integrity in 852 ft of open hole in the last sidetrack for
a production hole section. These treatments ultimately made it unnecessary to
set pipe early, which could have jeopardized the commercial discovery of the
lower gas sand. Earlier sidetracks attempted unsuccessfully to bypass the
loss/flow problems that would not allow drilling ahead and increasing the
18.0-lb/gal mud weight (MW) to drill into a high-pressure zone on a deep,
high-pressure/high-temperature (HP/HT) well in the western Gulf of Mexico shelf
in offshore Louisiana. Various conventional lost-circulation material (LCM)
treatments were used without success, increasing the hole’s pressure
containment.
The WPCI treatments raised the leakoff test (LOT) across the entire 852 ft
of open hole to 19.1 pounds per gallon equivalent (ppge) vs. the lower LOT of
18.26 ppge before the first WPCI job. LOTs were performed before and after each
of the two WPCI treatments to measure improvement in the open hole’s
pressure-containment integrity. This LOT data indicated that apparent fracture
gradients can be simultaneously increased in multiple rock layers with various
types of weak formations exposed in long, open holes by inducing near-wellbore
stress fields created from WPCI treatments (Webb et al. 2001; Kelley Sweatman
and Heathman 2001; Sweatman et al. 2001; Sanad and Waheed 2003). This approach
can then allow use of increased mud weights (MW) and drilling pressures to
prevent excessive gas influx from high-pressure sands without lost circulation
(LC) in adjacent weak zones.
Also discussed are the WPCI treatment design and job procedures, including
treatment optimization by the analysis of data from openhole wireline/logging
while drilling (OHWL/LWD) logs, cuttings lithology, fracture-seal location
indicators (torque on bit [TOB]/weight on bit [WOB]), and before/after LOT
pressures. Real-time operations (Kulakofsky et al. 2002) (also described)
enabled remote expert analysis and support so that wellsite personnel could:
(1) interpret formation characteristics for optimized treatment design, and (2)
analyze treatment pressure/rate data for selective placement of WPCI
sealants.
Background
The western shelf region in the Gulf of Mexico is known industry wide as one
of the most challenging areas in the world to drill for oil and gas. Faulted
formations, HP/HT conditions, abnormal pressure ramps, depleted reservoirs, and
LC are only a few of the major challenges operators encounter on a regular
basis. To deal with these issues, precise knowledge of well conditions and
carefully planned contingencies are required.
The structural map in Fig. 1 details the many faults associated with this
area. The well path associated with the example wellbore encountered many of
these faulted areas; the fault lines show why pressure-integrity issues were
encountered while drilling (Fig. 2). The main reason this well encountered so
many pressure-integrity problems was that the mud-weight window (MWW) was too
narrow.
Two weak zones were clearly identified before the WPCI job: one just below
the shoe at 17,628 to 17,710 ft measured depth (MD), or 16,038 ft total
vertical depth (TVD), and the other at 18,480 to 18,520 ft MD, or 16,679 ft
TVD. Before the WPCI treatments, the maximum MW of 18.0 lb/gal was too low to
hold back the lower production sand; as soon as the MW was increased, the well
began to lose fluid to these weak zones up hole.
A number of conventional LCM treatments were used in an attempt to stop mud
losses, but these had limited success and did not increase the WPCI of the well
(Webb et al. 2001; Kelley et al. 2001; Sweatman et al. 2001; Sanad and Waheed
2003; Kulakofsky et al. 2002; Wang et al. 2003; Sanad et al. 2004; Sweatman et
al. 2004; Wang et al. 2005). Finally, on the second sidetrack, two WPCI
treatments were used to increase the pressure-containment integrity from 18.26
to 19.1 lb/gal. These treatments allowed for an increase in the MW to 18.3
lb/gal with no losses and permitted drilling ahead through the production sand
to total depth (TD). Table 1 includes a summary of the well events and problems
encountered before WPCI treatments were applied.
Borehole Strengthening Approaches
An open hole’s WPCI may be increased to widen the MWW by various mechanisms
and materials. One of the challenges is to understand enough about the types of
formations in the open hole and the associated leak off flow paths to select
the best initial approach, rather than applying possible methods by trial and
error. The former approach can save significant amounts of rig time and well
costs vs. the latter, which can, and has, resulted in high costs (10 to 100%
over the AFE, or authority for expenditures), sidetracks, bypasses, and
abandoned wells. When offset well data is not available or applicable,
real-time measurements can be used to obtain the input data needed for an
analysis to determine the leak off flow path characteristics. This data
collection and analysis is explained in later sections of this article. The
results of the data analysis may provide the understanding needed for selecting
the most cost-effective approach.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
13 July 2005
- Revised manuscript received:
17 July 2006
- Manuscript approved:
13 October 2006
- Version of record:
20 March 2007
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