Inclined Loading Capacity of Embedded Suction Anchors in Clay

An analytical solution has been developed to estimate the inclined pullout capacity of an embedded suction anchor in clay seafloor. Validation has been made through comparisons with a limited number of centrifuge model test results. Results indicate that the inclined pullout capacity of an embedded suction anchor in clay decreases as the load inclination angle to the horizontal increases. As the point of the load application moves downward, the inclined pullout capacity increases, reaches its peak, and then starts to decrease.

Challenges in Hydrate Plug Prevention in Pipelines Seen Over the Lifetime of a Field

When the oil and gas industry explores subsea resources in remote areas and at high water depths, it is important to have advanced simulation tools available in order to assess the risks associated with these expensive projects. A major issue is whether hydrates will form when the hydrocarbons are transported to shore in subsea pipelines, since the formation of a hydrate plug might shut down a pipeline for an extended period of time, leading to severe losses. The industry practices a conservative approach to hydrate plug prevention, which is the addition of inhibitors to ensure that hydrates cannot form under pipeline pressure and temperature conditions. The addition of inhibitors to subsea pipelines is environmentally unfriendly and also a very costly procedure. Recent efforts has therefore focused on developing models for the hydrate formation rate (hydrate kinetics models), which can help determine how fast hydrates might form a plug in a pipeline, and whether the amount of inhibitor can be reduced without increasing the risk of hydrate plug formation. The main variables determining whether hydrate plugs form in a pipeline are: 1) the ratio of hydrocarbons to water, 2) the composition of the hydrocarbons, 3) the flowrates/flow regimes in the pipeline, 4) the amount of inhibitor in the system. Over the lifetime of a field, all 4 variables will change, and so will the challenge of hydrate plug prevention. This paper will examine the prevention of hydrate plugs in a pipeline, seen from a hydrate kinetics point of view. Different scenarios that can occur over the lifetime of a field will be investigated. Exemplified through a subsea field development, a pipeline simulator that considers hydrate formation in a pipeline is used to carry out a study to shed light on the most important issues to consider as conditions change. The information gained from this study can be used to cut down on inhibitor dosage, or possibly completely remove the need for inhibitor.

Experimental Evaluation of Separation Methods for a Riser Dilution Approach to Dual Density Drilling

A dual gradient, deepwater drilling system based on dilution of riser mud requires economically separating the riser mud into a low density dilution fluid and a higher density drilling fluid. This study investigated the practicality of accomplishing this separation using hydrocyclones and centrifuges and examined the possible benefits and efficiency of each. The separation experiments were conducted using a laboratory centrifuge and 2 inch hydrocyclones. The laboratory centrifuge was able to separate the riser mud into near ideal densities for dilution and drilling fluid. However, the dense slurry retained in the centrifuge had lower emulsion stability than the feed stream. The hydrocyclones achieved much less contrast in density between the low and high density discharges, but consistently resulted in a beneficial increase in the stability of the mud emulsion in all of the flow streams and had more desirable rheological properties. A qualitative comparison indicates that the hydrocyclone separation system may offer a feasible and desirable alternative to centrifuge separation system.

Calculation of Wave-Induced Shallow Stratum Seabed Slides in the Subaqueous Yellow River Delta

Wave-induced seabed slide could happen even at very gently sloping silty seabed. Based on the wave-seabed interaction, the safety coefficient calculation model of wave-induced gentle seabed slides in the seabed instability was carried out using limit equilibrium method, Bishop Method, in this paper. The calculated results shows that the effective internal cohesion c′ and the effective internal friction angle φ′ affect the location of slip surface and the magnitude of the safety coefficient significantly. The safety coefficient rises linearly with the increases of c′ and φ′ at a fixed depth. The results fit reasonable well with the slide calculation results from a wave flume experiment in laboratory. Additionally, it was concluded that the silty seabed tended to slide under wave actions at the depth less than 5 meters in the Yellow River Subaqueous Delta.

Effect of Drill-Ship Motions on Core Sample Conditions During the Nankai Trough Seismogenic Zone Experiment

The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1A, which is a part of the Integrated Ocean Drilling Program (IODP), is a series of expeditions in scientific drilling and coring operations aboard the first riser-equipped deep sea drilling vessel, Chikyu. The objectives are to recover good quality core samples and collect data on undersea properties and drilling conditions, which will also provide valuable information for future expeditions. The coring operations were carried out under harsh drilling and ocean conditions so that core recovery was inconsistent and fluctuated from high to low. Moreover, differences in independent lithology, depth, and the type of coring tools from previous expeditions made it necessary to analyze and optimize drilling parameters with new data. A serious concern in retrieving core samples was the vertical heave motions caused by the drill-ship since the active heave compensator system could not be activated before operations due to the extreme deep sea conditions and only the passive heave compensator was used. The drill string and coring tools are particularly vulnerable to the high heaving movements of the vessel so that the core recovery rate and quality are also adversely affected. The present work presents an analysis of geotechnical information, drilling parameters and the drill-ship motions the NanTroSEIZE expedition in order to optimize core conditions and maintain high core recovery.

A Modular Differential Dielectric Sensor (DDS) for Use in Multiphase Separation, Process Measurement and Control—Part II: Experimental Investigation

Accurate and continuous measurement of the percent water in crude oil production streams (watercut) over 0 to 100% range is critical for petroleum industry. High accuracy and stability are also required for surface measurement to support process control applications aimed at removing trace amounts of oil and particulates from produced water. This paper is a two-part paper — the first part [1] deals with analytical modeling of the Differential Dielectric Sensors (DDS) and the second part (current paper) discusses the results of key experimental investigations. A dedicated closed-loop experimental facility is used to obtain in-line real-time measurement of DD sensor data in a controlled configuration. A complete description of test facility is presented followed by detailed experimental results. The results show that DDS is unique in its use of very low noise and high sensitivity differential measurements between two identical sensors. In a process control system, DDS shows good measurement stability and is adaptive to composition measurements compensating for changes in oil composition, gas fraction, emulsion state, water NaCl concentration, temperature, and flow rate. Because of its auto calibration capability, DDS can also conduct real time calibration for sensor configuration changes caused by factors such as corrosion and erosion.

Utilization of Gas-Liquid Cylindrical Cyclone (GLCC©) Compact Separator for Solids Removal—Part I: Minimum Required Liquid Injection Rate

The hydrodynamic behavior of gas-liquid-solids in a modified GLCC© has been studied for the first time experimentally and theoretically. A GLCC© experimental facility has been designed, constructed and utilized to acquire data on gas-solid-liquid flow in both upstream 2-inch injection line horizontal section and in the 3-inch GLCC©. Experimental data have been acquired for the minimum gas velocity required to transport the solids up to the liquid injection point, and for the minimum liquid injection rate necessary to wet the solids and capture them in the liquid phase. The data have been acquired for 4 solid particle sizes of 5 μm, 25 μm, 50 μm and 150 μm. A mechanistic model has been developed or modified for solids transport/ separation, for the prediction of the minimum transport gas velocity, and the required minimum liquid injection rate. A comparison between the model prediction and the acquired experimental data shows good agreement. The average relative error for minimum transport gas and liquid velocities are, 4.3% and 9.55%, respectively.

Non-Darcy Binomial Deliverability Equations for Partially Penetrating Vertical Gas Wells and Horizontal Gas Wells

Many gas reservoirs are with bottom water drive. In order to prevent or delay unwanted water into the wellbore, the producing wells are often completed as partially penetrating vertical wells, and more and more horizontal wells have been drilled in recent years in bottom water drive gas reservoirs to reduce water coning and increase productivity. For a well, non-Darcy flow is inherently a near wellbore phenomenon. In spite of the considerable study that non-Darcy behavior of fully penetrating vertical wells, there has been no study of a partially penetrating vertical well or a horizontal well in a gas reservoir with bottom water drive. This paper presents new binomial deliverability equations for partially penetrating vertical gas wells and horizontal gas wells, assuming that only radial flow occurs in the near wellbore non-Darcy’s flow domain. The inflow performance of a vertical gas well is compared with that of a horizontal gas well. The proposed equations can account for the advantages of horizontal gas wells.

Laboratory Study on the Relationships Between Suspended Sediment Concentration and Electrical Conductivity

In order to find a simple, continuous method to determine the suspended sediment concentration in a high turbidity region, experiments were conducted to look for relationships between suspended sediment concentration and electrical conductivity. Sediments were sampled from the Yellow River Delta and a conductivity sensor was used to measure the electrical conductivity of different sediment content seawater. The influencing factors such as temperature and salinity are also investigated. The results show that good linear relationships exist between suspended sediment concentration and electrical conductivity; salinity and temperature have some influence on electrical conductivity, and salinity is the most important influencing factor and temperature takes the second place. Basically, the general linear regression formulas between suspended sediment concentration and electrical conductivity can be drawn with variable salinity and temperature. The relationships suggest that it is feasible to measure suspended sediment concentration in situ using electrical conductivity sensors.

A Coupled Finite Element-Element Free Galerkin Method for Liquefiable Soil-Structure Interaction Analysis Under Earthquake Loading

This study presents a numerical method for the seismic behavior assessment of liquefiable soil-structure interaction. In the method, the element-free Galerkin method (EFGM) is applied to simulate the behavior of the liquefiable sandy soil which will take place large permanent deformation under earthquake loading. The finite element method (FEM) is used to describe the behavior of the structure. Then, the EFGM and FEM are related by contact elements. The cyclic elasto-plastic constitutive model and updated Lagrangian large-deformation formulation are jointly adopted to establish the governing equations in order to take account for both physical and geometrical nonlinearities. The shape function is established by moving least squares method while hexahedral background cells are used. The essential boundary conditions are treated with the help of the penalty method. The coupled method can avoid the volumetric locking in the numerical computations using finite element method when non-uniform deformations happen. In order to assess the effectiveness and accuracy of the current procedure, numerical simulation of caisson-type quay wall subjected to earthquake motion is conducted.