Antonio C.V.M. Lage

Tuning of parameters in a two-phase flow model using an ensemble Kalman filter

A new methodology for online tuning of model parameters in a two-phase flow model by taking into account measured data is presented. Important model parameters are tuned using the ensemble Kalman filter. The present study is motivated by applications in underbalanced drilling, although the idea of using the ensemble Kalman filter in tuning of model parameters should be of interest in a wide area of applications. A description of modeling of the two-phase flow in the well is presented, as well as the implementation of the ensemble Kalman filter. The performance of the filter is studied, both using synthetic and experimental data.

Mechanistic model for upward two-phase flow in annuli

A mechanistic model is formulated to predict the mixture behavior for upward two-phase flow in concentric annulus. The model is composed of a procedure for flow pattern prediction and a set of independent mechanistic models for calculating gas fraction and pressure drop in bubble, dispersed hubble, slug and annular flow. Small-scale experimental data from the literature validate the predictions of the model. A full-scale experimental investigation is also executed to complete the evaluation. The experiments are performed in a 1278 m vertical well in the Petrobras research facility in Taquipe, Brazil, with an 88.9 mm x 159.4 mm (3.5 in, x 6.276 in.) annulus. Test matrix covered the whole range of possible combinations of liquid and gas injection rates for an underbalanced drilling operation in a similar geometry. The overall model performance is in good agreement with the experimental data.

Challenges and New Technologies for the Development of the Pre-Salt Cluster, Santos Basin, Brazil

Pre-salt carbonate reservoirs from Santos Basin represent a great opportunity and probably the most important recent oil discovery. Tupi area (estimated to have recoverable volume of 5 to 8 bboe), which is the most known amongst several other leads in the cluster, is going to be a great insight for the production project. From the production point of view, this new frontier has technological challenges that are being addressed by PETROBRAS and partners. Special attention is being dedicated to anticipate solutions to potential problems. This will require a balance between innovative and field proven solutions. This paper addresses the most critical points, where Petrobras is making a great R&D effort, which are: Well technology, where casing stability, well cost and productivity are addressed, in a scenario of water depths beyond 2,200m, target depths greater than 5,000m, crossing salt layers that can reach 2,000m in thickness. Poorly known microbial carbonate reservoir, heterogeneous in vertical profile, spread over very large areas, with wettability concerns, requiring careful evaluation of the performance of the waterflooding method and EOR. Wax deposition, due to low temperature in the ocean bottom, imposing limitations to the subsea layout. Gas processing and exporting technologies concerning environmental issues: CO2 compact removal units aiming the minimization of emissions to the atmosphere. Production units placed in more than 2,000m water depth, with oceanic conditions quite severe and dealing with high CO2 content stream. These challenges deserve all Petrobras attention, but also count with the confidence in achieving good technological solutions, supported by the history of successful developments of the company. Introduction The history of success built by Petrobras in deep water Brazilian coast – mainly Campos Basin – was largely supported by successive discoveries of heavy oil in turbidite sandstones, step by step towards gradually deeper and deeper water depths (Carminatti et al., 2009). The Pre-salt discoveries of Santos Basin represent discovery of huge volumes of light oil (28 to 30 degrees API), with high gas content, in a very short time span, close the most important consuming centers in Southeastern Brazil, and formation tests in the first wells have presented very high flow rates with no indication of barriers. All are excellent news, although PETROBRAS and partners recognize that the Pre-salt of Santos Basin represents a challenging scenario: ultra-deep water (greater then 2,000 meters), deep carbonate reservoirs (deeper than 5,000 meters), spread over very large areas, with high gas-oil ratio (GOR in Tupi area greater than 200 m/m), CO2 content (8-12% in Tupi), high-pressure and low temperature, laying immediately bellow a thick salt layer (more than 2,000 meters of salt), located around 300 km from the coast, with oceanic conditions more severe than Campos Basin. This scenario demands using sometimes present day technology in the limit, and other times, adaption and development of technologies specific for such conditions. This paper addresses the most critical points to the development of production in the Pre-salt of Santos Basin, where Petrobras is making an R&D effort to develop and qualify new technologies, including well technology, reservoir technology, flow assurance, gas processing and exporting technologies, and production units. Additionally, the paper discusses briefly how PETROBRAS has organized its structure to face these technological challenges, including the creation of a technological program – PROSAL – focused on Pre-salt objectives.

An overview of air/gas/foam drilling in Brazil

The air, gas and foam drilling has been used in specific areas in Brazil as an alternative for problems caused by the traditional drilling process. Considering those two-phase flow drilling operations, this work focuscs on their benefits and operational improvements. Furthermore, the comparison between the performance of conventional and two-phase flow drilling has bccn showing this new technique has some advantages: (1) minimum or no damage to sensitive pay zones. (2) immediate and continuous evaluation of cuttings for hydrocarbon shows, (3) avoidance of lost circulation, and (4) higher penetration ratcs in hard formations. Two very recent on-shore two-phase flow drilling field cases, one with joint pipe connections, and the other with coil tubing are mainly described Thcir results are analyzed concerning the surface equipment design, appropriate technique for connections when using drill pipe underbalanced drilling, as well as the comparison of predictions of computer programs to real field data. Future plans for the continuity of the two-phase flow drilling operations in Brazil are also commented. Additionally, potential areas and concrete actions for improving operational feasibility of this emerging technology are identified. The target is a safer and economical air, gas or foam drilling operation.

Free-Fall-Effect Calculation Ensures Better Cement-Operation Design

A cement-operation simulator was developed that takes the free-fall effect into account. This simulator allows prediction of well-fluid behavior and pressure, making proper field-operation design possible. The proposed mathematical model was derived from mass and momentum conservation laws by means of a macroscopic balance that reduces field equations to a 1D model. The resulting initial value problem is solved numerically with the Runge-Kutta method. Special care is taken to control the interfaces between two different fluids while the system is in free fall. A microcomputer program has been implemented with a user interface that permits complex well geometries. Other models are compared with the program to demonstrate its software capabilities.