Lost circulation is a major problem when drilling oil wells in Southern Mexico, where depths normally reach up to 7,000 meters with a fractured carbonate reservoir as the target. Very high mud losses reduces rate of penetration, increases cost of materials and induces other unwanted drilling events. Many times operators and service companies are forced to apply in-a-hurry lost circulation treatments mostly based on trial and error with very mediocre success. A Fiber system has been developed to cure lost circulation caused by the presence of natural fractures. The fiber system is deployed either in a spacer ahead of cementing or by spotting a pill during drilling. This Fiber system disperses readily in water-base fluids and is fully compatible with standard surface mixing and pumping equipments. This field study presents the application in Mexico of this innovative and resilient Fiber lost circulation system designed to mitigate the lack of characterization of the loss zone. Fourteen jobs performed and two applications described include pumping through commonly used BHAs during drilling, and as part of the spacer ahead of the cement slurry, when partial or total losses occurred with casing on bottom. Implementation of this engineered fiber-based lost circulation solution was extremely successful compared to the average success of other similar purpose systems. Particularly, two features were considered a breakthrough in applications while drilling: first, this solution saved 15 to 24 hours of rig time per operation as the BHA needs not be pulled out; and a second, and perhaps more important advantage consisted in being able to resume drilling quickly after pumping the material without risking to destroy the integrity of the seal. When used in a spacer ahead of cement in wells, where circulation was lost after getting the casing to its landing depth, the Fiber lost circulation solution allowed to successfully getting top of cement at the planned desired depth ensuring effective zonal isolation.
This paper describes the events leading to the collapse of a 9 7/8" liner over a 7 5/8" casing while drilling a depleted fractured reservoir (high inclination, 150°C BHST) using the concentric injection technique and Managed Pressure Drilling (MPD) in well "A" in the South of Mexico. It also illustrates the investigation process conducted aimed at the identification of the potential failure scenarios. Finally, a new casing design approach for wells under these challenging conditions based on limit state design and deterministic load estimate has been developed and implemented as a result.
This paper describes how the creation of an innovative multidisciplinary team - the Look Ahead Team (LHT) - together with ad hoc new built processes and protocols, have greatly helped minimizing both the geological and drilling risks and their impact in the very complex wells currently being drilled in the Mesozoico, Exploration and Alliance projects in Southern Mexico (MXS). Also, it explains how the integration of different knowledge domains coupled with detailed technical scrutiny, subsurface visualization, modeling and simulation, thorough multilayers risk assessments, risk management techniques, real time data acquisition and continuous application of lessons learnt, have been delivering substantial savings to the drilling operations. Wells can be classified as deep HP/HT and/or LP/HT wells. The objective of the LHT is to visualize and analyze drilling related risks, to generate alerts and recommendations before a new hole section is commenced, so that undesirable and detrimental subsurface events are anticipated and prevented or minimized. Drilling engineering, geology, geophysics, geomechanics and well placement are all represented in and form an integral part of the LHT. For each new well to be drilled, the geosciences' domain experts perform an integrated subsurface interpretation considering all current information available, offset wells and real time data. The analysis performed is twofold: a forecast drilling scenario (well trajectory and placement) which is optimized based on the calibration attained through the iteration with existing (offset) wells using sophisticated modelling and newly created work protocols that allow effective multidisciplinary workflows, subsurface assessment and detailed risk analysis by hole section. The main outcome of the analysis is to deliver a predictive ‘look ahead’ report which contains all risks identified at least 200 m ahead of the bit together with the risk analysis matrix and the corresponding prevention and mitigation plan. Also during the program execution, the LHT provides technical support to the engineering and operations teams anticipating the next action based on risk projection re-assessment using real data streaming. The Look Ahead Team's newly implemented processes/workflows and innovative analysis methodologies, have been tested on 21 development wells and 3 exploratory wells for a total of 72 hole sections. In just one year from its foundation, unforeseen drilling events due to geological uncertainty were reduced by 90% achieving 10MMUSD worth of savings.
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.
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