The Cantarell field is located offshore in the Bay of Campeche, in approximately 50 m of water depth (Fig. 1). The two main productive intervals are the Upper Cretaceous and Jurassic Kimmeridgian. The Cretaceous is highly fractured with well developed, vugular secondary porosity. The Jurassic is also fractured with oomoldic porosity. Both contain sour hydrocarbons. Production from Cantarell began in the early 1980s and today the pore pressure gradient is down to a +/− 0.37 gr/cc equivalent. The productive interval is typically drilled using a 0.90 gr/cc emulsion mud and shortly after penetrating the fractured reservoir, total and uncontrollable loss circulation is experienced. As a result, the cost of drilling in the field has increased considerably due to the high cost of the oil-in-water mud losses and time spent either transporting, generating or waiting on weather to offload more mud to continue drilling. Petróleos Mexicanos (PEMEX) in cooperation with Quantum Reservoir Impact (QRI) reevaluated the current drilling philosophy and recommended the application of a series of steps aimed at solving the current problems. The results obtained have been positive resulting in PEMEX now implementing such steps as part of its drilling philosophy where applicable on a regular basis. This paper will describe the current drilling environment and the techniques implemented in the first successful mud cap application in the Cantarell field. It will also discuss some of the lessons learned as well as the new improved designs being implemented and will conclude with a summary of the benefits obtained and the plans for the future.

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 completion 5 . 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 w...

The gravity drainage and oil reinfiltration phenomena that occur in the gas cap zone of naturally fractured reservoirs are studied through single porosity refined grid simulations. A stack of initially oil-saturated matrix blocks in presence of connate water surrounded by gas-saturated fractures is considered; gas is provided at the top of the stack at a constant pressure under gravity-capillary dominated flow conditions. An in-house reservoir simulator, SIMPUMA-FRAC, and two other commercial simulators were used to run the numerical experiments; the three simulators gave basically the same results. Gravity drainage and oil reinfiltration rates, along with average fluid saturations, were computed in the stack of matrix blocks through time. Pseudo functions for oil reinfiltration and gravity drainage were developed and considered in a revised formulation of the dual-porosity flow equations used in fractured reservoir simulation. The modified dual-porosity equations were implemented in SIMPUMA-FRAC,1,18 and solutions were verified, with good results, against those obtained from the equivalent single porosity refined grid simulations. Same simulations, considering gravity drainage and oil reinfiltration phenomena, were attempted to run in the two other commercial simulators, in their dual-porosity mode and using available options. Results obtained were different among them and significantly different from those obtained from SIMPUMA-FRAC. Introduction One of the most important aspects in the numerical simulation of fractured reservoir is the description of the processes that occur during the rock matrix-fracture fluid exchange and the connection with the fractured network. This description was initially done in a simplified manner and therefore incomplete.2,3 Experiments, theoretical and numerical studies 3–6 have allowed to understand there are mechanisms and phenomena such as oil reinfiltritation or oil imbibition and capillary continuity between matrix blocks that were not taken into account with sufficient detail in the original dual porosity formulations to model them properly and that modify significantly the oil production forecast and the ultimate recovery in a naturally fractured reservoir. The main idea of this paper is to study in further detail the oil reinfiltration phenomenon that occur in the gas invaded zone (gas cap zone) in NFR and to evaluate its modeling to implement it in a dual porosity numerical simulator. Considering the reservoir to be a stack of matrix blocks (sugar cubes) according to the Warren and Root 7 conceptual dual porosity model, the oil reinfiltration occurs when the oil confined in the upper blocks is expelled out of matrix blocks thru fractures and it reinfiltrates in the blocks below. This block to block oil flow occurs mainly because of the competition of the capillary and viscous forces. The study was divided in two parts, firstly using a single porosity simulator a fine grid was built in the space occupied by the stack of matrix blocks and fractures allocating the particular characteristics and properties of each medium to the different portions that these systems occupy in the grid. The phenomena that occur during the numerical experiment were studied. The capillary forces act only on the matrix blocks being zero in the fractures and the viscous forces are canceled out through the introduction of a very low gas injection rate through the top face of the stack; a flow process driven by capillary and gravitational forces only is established in this fashion. 8,9 In the fine grid simulation average gas and oil saturations are computed as time goes by for each one of the matrix blocks in the stack. Drainage and reinfiltration rates are computed through each one of the matrix block faces and their dependencies on the matrix block average gas saturations are established. Then the pseudo functions that are required in the modified dual porosity formulation are calculated. Secondly, using the modified dual porosity simulator SIMPUMA-FRAC, a coarse grid is built of the same dimensions of the single porosity fine grid and the gravity drainage is simulated by using the matrix-fracture transfer pseudo functions that had been previously generated. Hence, the modified dual porosity simulator should reproduce the average behavior observed in the fine grid for the stack of blocks in the single porosity model.