Summary
In southern Mexico, 65% of the oil and 74% of the gas production comes from
Mesozoic formations—naturally fractured carbonates—with a high potential for
loss of circulation. Lost circulation during drilling and cementing often leads
to formation damage and can severely impact well costs.
This paper describes the implementation of lightweight (9.17 lbm/gal)
slurries and a reticular-product technology to avoid losses while cementing and
to improve zonal isolation and post-cement job evaluation. Applying this
combination of technologies improved the success ratio of primary isolation of
the wells.
Lightweight cementing slurries with reticular systems were used in two wells
in Mexico: a development well (Copano 32) and an exploration well (Malva 201).
The wells were drilled underbalanced, and in both cases, lost circulation was a
problem during drilling and cementing. Using this technology, circulation of
the slurry was regained while cementing and returns reached the designed cement
top, avoiding an anticipated remedial cementing job. The pressure behavior
during cementing clearly showed the plugging effect of the fiber-laden slurry
in the formation; periodic low-pressure intervals were encountered before the
final constant increase in pressure, which indicated that the designed-cement
job objectives had been achieved.
In these wells, implementation of lightweight slurries and reticular-product
technology prevented further cement invasion into the production zone. Savings
in rig downtime and improved zonal isolation led to a significant reduction in
costs during the construction of the wells.
The cementing solution represented at least a 300% cost savings related to
the cementing process. He also confirmed that lightweight cement slurries with
reticular products are a viable solution for the depleted reservoirs, in
southern Mexico and similar wells around the world, in which lost-circulation
problems of this kind exist.
Introduction
Cementing production zones characterized by lost circulation present
numerous problems not easily solved during and after the cementing operation.
Extra cost and formation damage are some of the consequences of lost
circulation, which operators have to deal with during the construction and
completion stages of the well.
In this case, this particular set of lost-circulation issues exists in an
area in Mexico called the Mexico south region, located onshore near the Yucatan
Peninsula (Fig. 1). The principal operator is a state-owned oil company. Zonal
isolation in wells in this area is a challenge for cementing operations because
of the reservoir characteristics. In the Mexico south region, 74% of gas
production and 62% of crude production comes from naturally fractured zones in
Mesozoic carbonate strata.
These zones have high-conductivity channels; consequently, lost circulation
occurs during drilling and cementing. These losses create a series of problems,
including poor cement bond between annulus and liner, the need for remedial
cementing jobs, increased blowout risk, and formation damage—all of which
require extra money and time.
The application of new technology, in addition to adequate slurry selection,
provided an opportunity to achieve successful primary cementing jobs in the
Mexico south region. Several techniques have been previously applied to try to
solve the problems; for example, foam cement was as an initial solution because
of the lightweight characteristics of the system. However, this system failed
to meet the mechanical requirements for a proper hydraulic seal and the
designed placement of the cement in the annulus. In 90% of the cases, remedial
jobs had to be carried out to fill the annulus with the correct column of
cementitious material needed for the completion of the well.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
13 September 2004
- Revised manuscript received:
18 October 2005
- Manuscript approved:
11 November 2005
- Version of record:
20 September 2006
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