1D Mechanical Model Research Articles

The fluid flow modeling procedure including a critically stressed fracture analysis of coalbed methane reservoir: a case study of Upper Silesian Coal Basin, Poland

The geomechanical modeling turned out to be an essential component of the hydrocarbon exploration assisting reduction of risk of drilling issues and optimization of hydraulic fracturing treatment. This study provides a workflow of critically stressed fracture (CSF) analysis dedicated for coal layers. The main focus of the paper is applying the 1D mechanical models and following modelling of hydraulic fracturing treatment to describe the fracture behavior under the impact of the stresses at the wellbore scale. Another objective of the presented study is demonstration of benefits of 1D and 3D CSF analysis to understand fracture contribution to gained volume of hydrocarbon after fracturing of coal seam. Interpretation of fracture orientation and their behavior is vital to effective development of coal bed methane (CBM) resources as the CSF can be responsible for considerable part of CBM production. Natural fractures and faults contribute to fluid flow through rock. It is often noted that natural fractures may not be critically stressed at ambient stress state. However, during stimulation, the optimally oriented natural fracture sets have the inclination to become critically stressed. Hence, understanding of the recent stress state and fracture orientations is significant for well planning and fracturing design. The outcome of this study are comprehensive 1D mechanical Earth models (MEMs) for analyzed wells and explanation of behavior of identified CSF under variable stress state as well as understanding of the connectivity of natural fractures within zone subjected to fracturing treatment.

Correction of cavitation with thermodynamic effect for a diaphragm pump in organic Rankine cycle systems

Diaphragm pumps are a sort of leakage-proof reciprocating pumps with low flow rate but high head and better efficiency, and can potentially find their applications in organic Rankine cycle (ORC) systems as the feed-pump of organic fluid to the evaporator. A diaphragm pump in an ORC system may suffer from cavitation in the pump suction chamber inevitably when the pump delivers an organic fluid. However, the cavitation performance of the pump has been a little known for organic fluids so far. In the article, the performance of a specific diaphragm pump was determined based on the existing performance charts provided by the pump manufactory in terms of pump rotating speed and inlet liquid pressure for cold water. The net positive suction head required (NPSHr) was predicted by involving thermodynamic effect in cavitation when the pump feeds the organic liquid R245fa to the evaporator in an ORC system at 480rpm rotational speed. The net positive suction head available (NPSHa) was calculated at 100 kPa and 141 kPa inlet liquid pressures, and the corresponding cavitation safety margins were addressed. The subcooling for the NPSHr and NPSHa as well as the safety margin were figured out. Two one-dimensional (1D) mechanical models for motion of the suction valve were built and solved at 480rpm and 100 kPa and 141 kPa inlet pressures. A preliminary experiment was performed to verify the analytical results. It turned out that the NPSHr is reduced to 2.02m from 3.02m NPSHr of cold water due to the thermodynamic effect in cavitation, and the corresponding subcooling is lowered to 8.28 °C from 12.38 °C. 100 kPa but 141 kPa inlet pressure can result in cavitation in the pump. The 1D mechanical models are subject to a rough spatial resolution for the flow field in the suction chamber, hence three-dimensional(3D) numerical simulations of the flow field are desirable.

Mechanical models for shear behavior in high damping rubber bearings

High damping rubber bearings have been in use for seismic isolation of buildings worldwide for almost 30 years now. In the present work, a brief introduction to the process leading to their manufacturing is first given. Next, a series of novel 1D mechanical models for high damping rubber bearings is proposed, based on the combination of simple and well-known rheological models. These models are calibrated against a set of harmonic tests at strain amplitudes up to 200%. Extension of the models to bidirectional horizontal motion and to time-varying vertical loads is the subject of ongoing work.

Modelling the effect of climate change induced soil settling on jointed drinking water distribution pipes

Soil settlements related to groundwater lowering are expected to be accelerated by climate change and may damage underground infrastructure networks. A 1D mechanical model, previously developed for continuous pipelines, has been extended towards jointed pipelines to calculate the stresses and joint rotations induced by the soil settlements. From the mechanical model, curve fits were acquired that can be used to estimate the bending moments and joint rotation. The curve fits differ per soil type, joint stiffness, joint position and joint distance. The stresses calculated by the 1D mechanical model and curve fits were validated by means of 3D finite element modelling. Using the curve fits, a probabilistic approach was followed by means of a Monte Carlo method to calculate the probability of failure of the pipeline system. The effect of joints is that the pipe stresses are reduced as the joints absorb a part of the soil displacement. For the probability of failure, the pipe stresses have a larger contribution than the joint rotation, as the joint rotation remains small compared to the maximum allowable joint rotation.