Alvaro Maia da Costa

GEOMECHANICS APPLIED TO THE WELL DESIGN THROUGH SALT LAYERS IN BRAZIL: A HISTORY OF SUCCESS

The lessons learned on the geomechanical salt behavior and its application in subsalt wells design are described in this article. In addition, the developed methodology validation, through comparison between computing modeling results with measurements carried out in experimental panels, in the potash mine, and with measurements obtained in an experimental well drilled for the purpose of calibrating and optimizing directional drilling in salt layers are presented. These parameters and methodology have been used for supporting the design of the wells drilled in the Pre-Salt giant oil fields in Brazil with very successful results.

Soil-Structure Interaction of Heated Pipeline Buried in Soft Clay

Heated pipelines buried in soft clay can develop a very challenging behavior. The thermal expansion of the pipelines normally induces buckles, which will be supported by the passive soil reaction. The buckles of the pipelines in soft clay can generate a non-linear inelastic behavior that is an unstable situation named “snap through”. In such situation the pipeline can jump from a configuration of a few centimeters displacement to another of meters displacement. Once the snap through situation has developed, there is the possibility of a local pipeline buckling, causing the pipeline rupture and as a consequence an oil spill. This paper presents the results obtained during the analysis of the rupture of a buried heated pipeline in the Guanabara Bay of Rio de Janeiro, Brazil. A very sophisticated procedure including a simulation of the thermal mechanical interactions between the soil and the pipeline structure was developed for back analysis of the thermal inelastic pipeline buckling. Computer modeling was carried out using the finite element method considering of the non-linear material behavior of the soil and pipeline, and nonlinear geometrical behavior of the pipeline. A cyclic thermal-mechanical soil-pipeline structure interaction model was the challenging aspect of the simulation, that explains the trigger mechanism of the snap through behavior of heated pipelines, which was responsible for the rupture of the pipeline in Guanabara Bay.Copyright

HP-HT Pipeline Cyclic Behavior Considering Soil Berms Effect

This article presents a numerical study for the Petrobras HP-HT pipeline P-53/PRA-1 that will be installed at Marlim Leste field in Campos Basin offshore Brazil. This pipeline will connect P-53 platform in deep-water (1031m) to an Autonomous Platform for Intermediate Pumping (PRA-1) in shallow water (100m). HP-HT pipelines resting on seabed can develop thermal buckling, which is an important concern for the pipeline structural integrity. The aim of this study is to verify the P-53/PRA-1 pipeline behavior during lateral buckling due to thermal cycles and pressure variations, using a new approach for the pipe-soil interaction model in contrast with the traditional Mohr-Coulomb friction model. The pipe-soil interaction model considers soil berms formed due to pipe cyclic displacements, representing different phases of the soil lateral reaction force versus displacement curve: breakout force, suction release, berm formation and residual resistance. The results presented compare the traditional Mohr-Coulomb model with the proposed one for several loads cycles, analyzing displacements, stresses and strains behavior during thermal buckling.Copyright

Experimental Tests and Numerical Simulation in a Reduced Model in a Pipeline With ZIG-ZAG Geometry: A Parametric Study

In January 2000, PETROBRAS faced a leakage of heavy heated MF380 oil from a 0.406m pipeline in the Guanabara Bay. When interacting with the soil, the thermal structural buckling of the pipeline induced the rupture of the pipeline wall causing the oil to leak. In order to overcome this undesired phenomenon, PETROBRAS studied several new pipeline alternatives. As a result of these studies, a “ZIG-ZAG” geometry pipeline named PE-3 was adopted. Given that the oil industry applications of this kind of concept have been very few and in soil conditions different from the ones in the Guanabara Bay, a very sophisticated procedure was developed including the simulation the thermal mechanical interactions between the soil and the pipeline structure. Computer modeling was carried out using the finite element method considering the soil, the pipeline non-linear material behavior and the finite displacements. In order to validate the numerical modeling, an experimental test was carried out in a reduced model with physics similar to a ZIG-ZAG geometry pipeline (PE-3). The numerical and experimental results match and have a fine conformity. After validation of the models, numerical and experimental parametric studies were completed with various angles and wavelengths of ZIG-ZAG to evaluate the conception of the PE-3 pipeline.Copyright

Global Buckling of a Heated Pipeline in the Campos Basin Brazil in a Region With Free-Spans

This article presents the behavior a heated flowline in Campos Basin-Brazil that crosses an uneven seabed region with free-spans of different lengths. In that region the mean water depth is arround 900 m and the pipeline supports the highest temperatures. A regular inspection with ROV (Remote Operate Vehicle) showed that the flowline is interacting with the surrounding soil, evidencing movements due to thermal expansion. Geotechnical survey showed that the soil in the pipeline route is composed by normally consolidated clay where the strength properties were obtained by CPT interpretation. The principal question for the pipeline operator concerns the pipeline integrity despite of the evidence of thermal buckling occurrence. In order to answer this question, a 3D finite element model was generated considering lateral imperfections, free-spans and pipe-soil interaction along the pipeline route obtained by ROV. A complementary inspection was done with Side Scan Sonar Image obtained by AUV (autonomous Underwater Vehicle), mapping lateral buckles and the free-spans in the pipeline route. The bending moment and effective axial force in the pipeline obtained by 3D finite element global model were used to verify the pipeline integrity based on DNV OS-F101 standard [1]. In order to verify the vertical buckling in the free-spans, a parametric study was done with different free-spans and feed-in lengths based on geometry acquired from inspections. This study supplies the critical temperature variation that triggers thermal buckling in the free-spans, enabling the determination of the critical free-spans in the flowline route. The results obtained by finite element modeling was the definition of the maximum operating temperature and pressure that enables operate the flowline safety based on DNV OS-F101 code.Copyright

Application of the ZIGZAG Concept to a Heated Pipeline in the Soft Soil of the Guanabara Bay

In January 2000, a buckling caused by a thermal expansion of a pipeline in the Guanabara Bay/Rio de Janeiro led to the rupture of a 16” pipeline to the leakage of heavy heated MF380 oil into the bay area. In order to avoid such undesired incident, PETROBRAS has carried out research looking for solutions for a new pipeline. As a result the concept of a pipeline with “ZIGZAG” geometry was introduced. There are very few examples of oil industries that apply this concept, especially with the soil conditions of the Guanabara Bay. Several studies were carried out to verify the thermal stability of this new pipeline structure. This paper presents a comparison between the conventional single pipeline and the ZIGZAG pipeline.Copyright

Pipeline Visualization, Simulation and Monitoring in Unstable Areas Affected by Soil Movements at Serra do Mar – Brazil

In this work we discuss the importance of visualization, simulation and monitoring pipelines constructed in areas geologically unstable. In particular it is of great concern pipelines crossing Serra do Mar, in Brazil, where there are colluvium deposits subject to slow movements not traceable by a simple visual inspection most of the times. In order to guarantee the structural integrity of the pipeline it is necessary to measure the tensions transmitted by the ground to the pipeline. Knowing that the soil-pipeline interaction is extremely complex the implementation of an extensive program involving visualization, simulation and monitoring that includes not only the slope but also the pipeline becomes mandatory. This program seeks the collection of information that allows the establishment of a reliable interaction model. This model must be capable of providing operational control parameters and subsidize the decision of an intervention in the pipeline. Therefore the safety of pipeline operations can be maximized through instruction of operators and establishment of monitoring and inspection routines. Right now, in a joint effort of CENPES and TRANSPETRO, a complete set of visualization and numerical simulation software platform is available and it is being used to build a 3D model of all the geotechnical risky areas in Serra do Mar. Also the installation and operation of a pilot monitoring system, including piezometers and inclinometers on the slope and strain gauges on the pipeline, at three different pipelines crossing Serra do Mar, with data acquisition in real time is being undertaken.Copyright

A finite element approach of the hydraulic fracturing technique for oil well stimulation

The hydraulic fractioning technique for oil well stimulation has been worldwide used and requires practical experience and geotechnical knowledgement. The first step in the work is the stress distribution analysis to establish the hydraulic pressure to be applied inside the well which will provide the required fracture system. This paper covers the application of finite element method for stress analysis considering adequate boundary conditions for simulation of underground excavations in an infinite medium, by the application o f special elements. The stress distribution analysis is actually the simulation of the effect of well boring taking into account the fluid pressure inside the well and the fluid pressure inside the rock mass when a penetrating fluid is considered. The material behavior is considered to be elasto-plastic according to the yielding criterium of Mohr-Coulomb. At the elastic region comparisons are made with analytical solutions available.