Instrumented Deep Tubing Tail Completion: A Good Practice For Monitoring Cantarell Reservoir's Behavior
Authors: Ladrón de Guevara T. , Ernesto J. , González-Vázquez Marcela , Posadas-Mondragón Ricardo 
Published: April 2012

As part of the efforts to increase the productive life of wells in the Akal Field, new completion alternatives and major workovers have been investigated. Drilling horizontal wells was considered at the beginning of 2006 in order to maximize contact with the reservoir. The goal was to reduce the pressure drawdown at the bottom of the well and delay the water-oil and gas-oil contact movement; however, a new issue was found: the high quantity of the almost vertical fractures that the horizontal wells intersected in their trajectories were connected to either the aquifer and/or the gas cap. This led to consider different types of horizontal completions that would address this issue. The completions design was equipped with blank pipe sections intended to isolate the fractures and passive inflow control devices to force a uniform pressure drawdown along the horizontal section. In spite of all these considerations, undesirable results were observed in some wells because in the field it was not possible to isolate 100% of the above mentioned fractures. As a result, they ended up producing high water cuts or high GOR.

Recently a new type of completion has been implemented in Cantarell. It is known as the deep tubing completion5. The application in Cantarell consists of leaving the last 60 to 600 meters of hole section open through the Upper Cretaceous Breccia crossing the gas cap and landing inside the oil window. The completion consists of setting up a packer/hanger with a tubing extension (tail) leaving it between 2 to 5 meters from the bottom of the borehole. The packer/hanger is anchored in the last cemented casing string (Paleocene). The tail is made out of either open ended production tubing or slotted liner which allows the fluids to flow from the bottom of the hole only. After several successful deep tubing completions, Pemex decided to install sensors in the completion string to monitor and control the well in real time. The well selected for this application was Cantarell-3054 which was instrumented with four sensors to monitor the behavior of gas, oil, and water while the well was on production. The results have been exciting as it is shown in this paper. These types of completions have been used all over the world, including the Middle East and the Yates Field in Texas where it takes its generic name.

The long open hole sections used in this kind of completions is benefited by the gravity drainage process, resulting in an improved production performance; especially in formations highly fractured with high productivity indexes such as the Upper Cretaceous Breccia. Simply stated, the deep tubing completion has the capacity to collect the oil being drained from the shallower gas zone and to produce it at the bottom open hole.

The implementation of this technique has been a success in the supergiant Akal field in the Cantarell Complex. From 2010 to date, 23 completions of this kind have been implemented. Out of these, only three have underperformed. Two of these were completed in the Lower Cretaceous horizon where the productivity and rock quality are much lower than in the Upper Cretaceous Breccia.

These types of completions also facilitate monitoring the water-oil and the gas-oil contact movement in the reservoir. The pressure and temperature instrumentation included in the deep tubing completion allowed monitoring of fluids contacts movement and fluid gradient changes. From these data the bottom hole pressure drawdown is computed and the critical rate of the well is estimated in order to avoid potential conning of water and/or gas.

This paper shows how the pressure behavior was recorded in real time during the first application of an instrumented Deep Tubing Tail completion in Cantarell 3054. The completion was equipped with 4 sensors. Three sensors were originally in the oil zone and one in the gas zone. At the time of writing this paper, 2 of the sensors are in the oil zone and 2 in the gas zone.