Preventing Lost Circulation by Use of Lightweight Slurries with Reticular Systems: Depleted Reservoirs in Southern Mexico
- Salvador Romero (Pemex) | Rafael R. Monroy (Pemex) | Carl R. Johnson (Schlumberger) | Francisco Cardenas (Schlumberger) | Gustavo A. Torres Abraham (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 2006
- Document Type
- Journal Paper
- 185 - 192
- 2006. Society of Petroleum Engineers
- 1.14.3 Cement Formulation (Chemistry, Properties), 1.6 Drilling Operations, 1.14.4 Cement and Bond Evaluation, 5.8.7 Carbonate Reservoir, 1.8 Formation Damage, 1.14 Casing and Cementing
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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.
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.
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