Successful Application of Automated Choke MPD System to Prevent Salt Water Kicks While Drilling in a High-Pressure Tertiary Salt Diapir with OBM in Southern Mexico

Abstract

The field subject of this paper is located in the southern Mexico, 34 km North of Villahermosa, Tabasco. Oil exploitation targets the Cretaceous and Jurassic formations (4500 mts a 5200 mts TVD). The 12 ¼" section of these wells must be drilled through a high pressure tertiary salt diapir which historically has been a high NPT generator due to high pressure salt water kicks and OBM contamination. Drilling strategy is usually oriented to the use of high density inverse emulsion mud with densities normally ranging between 1.95 to 2.27 SG (16.2 to 18.9 ppg). High density mud causes losses in the interfaces above and below the salt diapir and in some cases losses while drilling the salt diapir due to sand intercalations. A close analysis of the offset wells identified the MPD as a possible solution to mitigate the risks confronted in the section. This document describes the first application of the automated choke MPD system in Mexico, in a Sen well, and how the use of automated choke MPD system allowed drilling the section with no major operational events such as influxes, losses, stuck pipe or salt water contamination of OBM. The system helped detecting micro influxes giving tangible added value to this challenging narrow mud window hole section. As a result 938 meters of salt were drilled in only 11 days while field average is around 30 days. Introduction The field named "Sen" is surrounded by several other producing fields, Escarbado, Melocotón, Cardo (north boundary), Menta (west), Catarroso, Escuintle and Ricino (east) and Musgo (south boundary) (Fig. 3.2.1). Such field was discovered in 1984 with exploration well Sen 1 and its production began later in 1987 when the infrastructure was installed. The field has a drainage area of 29 km2, and an average thickness of 685 m with 229 m average net thickness. Productive formations are Upper, Medium and Lower Cretaceous, which are mainly comprised of mudstones, and the Jurassic which produces from dolomites. The hydrocarbon production comes mainly from the Upper Medium Cretaceous fractured reservoirs. The field is highly fractured and produces light crude of approximately 40° API. In terms of permeability and connectivity, it presents a high level of anisotropy. Production mechanism is water drive and the oil water contact (OWC) was determined at 5650 m.b.n.m.