Cláudio dos Santos Amaral

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

Closed-Ended Pipe Piles: Testing and Piling in Calcareous Sand

This paper reviews experience gained with large closed-end piles in the Campos Basin, offshore Brazil. Non-conventional solutions were tested and the closed-end concept found to be feasible. Finite element analysis was used to verify the optimum cone-geometry tip and the compacted soil mass zone due to pile group driving. The installation of 72 piles with 66 inch and 80 inch outside diameter showed this to be a very appropriate solution for pile foundations in similar soils of carbonatic origin, without very high bearing-capacity superficial layers.

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

Shear-Strength Signatures of Mass Movements, Continental Slope of Campos Basin, Brazil

Downhole shear-strength profiles, obtained from cone-penetrometer and lab tests were tied to sedimentary facies from adjacent continuous cores. The geotechnical response of mass-transport deposits was investigated. In the Campos Basin, sediments have evacuated from the upper continental slope and have accumulated as folded deposits on the middle slope. Sediment removal is recognised by an abrupt step-like change in shear-strength at the level of the unconformity. The folded deposits are characterised by a belly-shaped increase in shear-strength coinciding with a zone of intense lamination within the deposit, induced by internal shearing and fluid loss (strain hardening). In contrast, highly disintegrated muddy debris-flow deposits are indistinguishable, in terms of shear-strength, from normal hemipelagic slope sediments.

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

Using Tension Measurement Methods for Backfill Procedures in the Evaluation of Pipelines

The OPASC and the OSPAR are 10″ and 30″ pipelines, respectively, which interconnect the State of Santa Catarina and Parana, crossing the Serra do Mar, in southern Brazil. In 2003, after conducting slope stabilization works on a point of geotechnical activity, vibrating string gauges were installed to monitor the stress in these pipelines, in addition to geotechnical instruments installed to monitor the slope. These gauges were installed in seven sections, with 3 instruments per section, along a span of 180 meters.Although the geotechnical instrumentation has shown no evidence of movement in the slope, the gauges recorded an increase in stress values in some of the sections within three months from the time of installation, however, they remained stable in their values for the next ten years. In 2013, blind hole tests were performed to determine the stresses in these sections and to verify the proper function of the gauges. The combination of these two measurement techniques, vibrating string gauges and blind hole tests, allowed for the determination of the stress state in sections, over time. From there, equivalent stress could be determined and compared with allowable stresses defined in standards.After the completion of the blind hole test and subsequent backfill, stress rose again at the same rate, returning to the level reached after the initial installation of the strain gauges. To reduce the stress level additional excavations have been made to relieve the stress on the pipeline, followed by backfilling performed in a controlled manner in order for the soil to properly compact, which reduced the stress value over the pipes. The graphs depicting variation over time of stress showed a significant reduction in the level of stress after the backfill.The main conclusions are listed as follows: a) the evolution of stress observed by the extensometers was primarily caused by pipeline settling; b) the vibrating string gauges are functioning properly and provide reliable readings even after ten years of service; c) the blind hole testing performed in conjunction with monitoring by vibrating string gauges can provide approximate values of the full stress state; d) after stress relief, backfilling of the trench must be carried out by compacting the soil beneath the pipe in order to reduce bending stresses due to the weight of the soil; e) backfilling of the trench, when not properly performed, can cause compressive stress in bending, reaching 390 mPa over the next few months.Copyright

Susceptibility to Erosion of Pipeline Rights-of-Way in Tropical Soils: Case of a Brazilian Pipeline

TRANSPETRO is responsible, among other activities, by operation and maintenance of pipelines throughout Brazil. Particularly in the Midwest region the company operates the OSBRA pipeline, which moves about 8.7 Mm3/years of fuel and covers approximately 1,000 km long, predominantly in tropical soils. Erosive processes are significant and constitute the main geotechnical occurrence in OSBRA pipelines rights-of-way. In order to identify the susceptibility to erosion of the area close to the pipelines were developed basic thematic maps, that overlaid will help in identifying homogeneous zones in terms of existing material susceptibility. The mapping is being accompanied by an extensive endeavor of field inspections along the pipeline rights-of-way, that comprised geotechnical investigations, verifying the conditions of use and soil management, the conservation status of existing drainage works and geotechnical characterization of soil samples of major geological formations, including erodibility tests. The methodology is being developed in ArcGIS frame, starting from the morphometric analysis and the use of Digital Elevation Models (DEM), aiming to understanding superficial flow conditions (acceleration and concentration) and consequent soil loss. The modeling results will be compared with historical occurrences erosive 15 (fifteen) years of pipeline operation, seeking for an adherence on various geological, topographical and meteorological tested. The methodology will improve further procedures for identifying potential erosions in tropical soils and will allow to anticipating preventive maintenance in the most susceptible locals the pipeline rights-of-way, suggesting mitigation measures best suited for each type of potential erosive mechanism.Copyright

An Inverse Numerical Technique to Estimate the Undrained Shear Strength of Marine Clays in Deep Waters

The study of alternative techniques to characterize the geomechanical properties of marine clays in deep waters has been the objective of numerous studies. Such research is warranted because of the difficulty in the use of traditional inspection methods under those environmental conditions. This paper presents an inverse numerical technique to evaluate the undrained soil shear strength of the marine soil. This technique is based on the response measurement during penetration in the marine soil by a gravity released pile. By inverse here we mean that the algorithm developed uses the experimental data to fit the parameters of the differential equation of motion of the pile during the penetration, using the least square method. In this procedure the parameters are associated to the undrained shear strength of the marine clay and to the drag coefficient of the pile. Examples are shown to illustrate the feasibility of the method when compared to other conventional tests.Copyright