RIASSUNTO
Abstract
This paper describes lessons learned and results obtained while applying a rotary drilling with liner system on conventional rigs, during the planning, design and drilling operation in offshore wells located in the Mexican coasts of the Gulf of Mexico.
Due that the cretacic formation named El Abra is composed by naturally fractured limestone and since its structural top (origin reef) has been eroded, it is difficult to detect it. Moreover, the differential pressure between the Tertiary and El Abra, result in several hole problems, such as: severe lost circulation, stuck pipe, cave-ins of holes and bad casing cementing jobs. These problems have increased time and cost in the drilling projects.
Continuous searching for alternative solutions with new technology to solve specific problems in the drilling process, lead PEMEX Exploration and Production to apply the non conventional option of rotary drilling with liner, meeting the safety standards established by the company.
The applied drilling with liner system, has allowed to drill down to the objective depth with high angle, cement the liner and drill out the following interval horizontally, steering in the reservoir. The system consists of a shoe drillable bit, a float collar, stabilizers, a liner with integral flush connections of high torque and a rotary liner hanger.
The results of the technique are presented utilizing a liner of 9 5/8?? and a bit of 12 ¼??, also hydraulic analysis, stress generated in the casing and the connections by 75° angle of hole construction, torque and drag, and drilling parameters. A comparison with conventionally drilled wells is performed, pointing out the problems found in the field, the results achieved, and how by applying the technique drilling with liner, savings of 40 days time and 5.0 MM usd per well, have been accomplished.
Introduction
Eight fields have been developed in the offshore Faja de Oro Golden Lane (Arrecife Medio, Isla de Lobos, Tiburon, Bagre, Atun, Morsa, Escualo and Marsopa), having a cumulative production of 210 MMBOE. These fields have produced light crude ranging from 30 to 40° API, from El Abra Middle Cretaceous limestone.
In May 1972, the Carpa 1 well was completed, located on a structure detected with 2D seismic. This well turned out to produce from El Abra Formation, which was found at 8,013 ft. In the formation test done on this well, rates of 503 BOPD of 33° API, light crude, were recorded together with 0.188 MMSCF/D associated gas.
From 1996 to 1997, 350 square miles of 3D seismic from the Faja de Oro offshore cube were acquired. The structural configuration generated from the 3D seismic revealed that the Carpa 1 well was located on the Western flank of a high that formed a stratigraphic trap of the depositional paleo relief type modified by erosion. This interpretation also allowed a better choice for the location of the Carpa 101 well, which found the top at El Abra 121 ft higher than Carpa 1.
Carpa 101 well was drilled and completed at the 7,865 - 8,102 ft interval, and plugged due to borehole instability. An openhole sidetrack was performed drilling a horizontal section into El Abra Formation. The well produced at a maximum measure rate of 4,814 BOPD of 32° API and 0.613 MMSCF/D. In the gage flow tests the well was shut down awaiting the production export pipe line.
Location
The Carpa Field is located on the Continental Shelf of the Gulf of Mexico, off the coast of Northern Veracruz, between the Tuxpan port and the Tamiagua lagoon 19 miles away from the sea coast, at a water depth of 154 to 174 ft. It is geological located on the Eastern edge of the Tuxpan Cretaceous shelf, on the El Abra play within the Tiburón-Esturión area. The project lies between the crests shown in Figure 1.