scholarly journals Borehole enlargement rate as a measure of borehole instability in hydrate reservoir and its relationship with drilling mud density

2021 ◽  
Vol 11 (3) ◽  
pp. 1185-1198
Author(s):  
Qingchao Li ◽  
Lingling Liu ◽  
Baohai Yu ◽  
Linian Guo ◽  
Sheng Shi ◽  
...  
Keyword(s):  
Natural Gas ◽  
Drilling Fluid ◽  
Coupling Model ◽  
Fluid Density ◽  
Drilling Mud ◽  
Borehole Stability ◽  
Hydrate Dissociation ◽  
Hydrate Reservoir ◽  
Fluid Seepage ◽  
Model Fluid

AbstractBorehole collapse will pose a threat to the safety of equipment and personnel during drilling operation. In this paper, a finite element multi-field coupling model for investigating borehole collapse in hydrate reservoir was developed. In this model, fluid seepage, heat transfer, hydrate dissociation and borehole deformation are all considered. Based on which, effects of drilling fluid density on both of hydrate dissociation and borehole collapse are investigated. The investigation results show that disturbance of drilling fluid invasion to hydrate reservoir will lead to hydrate dissociation around wellbore, and dissociation range narrows obviously with the increase in drilling fluid density. When the relative fluid density is 0.98, natural gas hydrates in reservoir with a width of about 16.65 cm around wellbore dissociate completely. However, dissociation range of natural gas hydrate has decreased to 12.08 cm when the relative fluid density is 1.10. Moreover, hydrate dissociation around wellbore caused by drilling fluid invasion may lead to borehole collapse, and borehole collapse can be significantly restrained with the increase in relative fluid density. Borehole enlargement rate is 33.67% when the relative fluid density is 0.98, but nearly no collapse area displays around wellbore when the relative fluid density increases to 1.12. In addition, investigation herein can provide an idea for designing drilling fluid density in hydrate reservoir when different allowable borehole enlargement rate is considered. The minimum fluid density designed for avoiding disastrous borehole collapse increases nonlinearly when higher requirements for borehole stability are proposed.

scholarly journals Dynamical well-killing simulation of a vertical H2S-containing natural gas well

2020 ◽  
Vol 75 ◽  
pp. 71
Author(s):  
Liangjie Mao ◽  
Mingjie Cai ◽  
Qingyou Liu ◽  
Guorong Wang
Keyword(s):  
Natural Gas ◽  
Drilling Fluid ◽  
Coupled Model ◽  
Transient Temperature ◽  
Fluid Density ◽  
Gas Well ◽  
Hole Pressure ◽  
Bottom Hole Pressure ◽  
Bottom Hole ◽  
Casing Pressure

This work aims to explore the dynamical well-killing process of a vertical H2S-containing natural gas well. A dynamical well-killing model considering an H2S solubility was established to simulate the overflow and well-killing process of a vertical H2S-containing natural gas well. The mass and momentum equations of the coupled model were solved using finite difference method, while the transient temperature prediction model was solved using finite volume method. The coupled model was validated by reproducing experimental data and field data of Well Tiandong #5. The effect of H2S content, mud displacement, drilling fluid density, and initial overflow volume on the dynamical well-killing process of an H2S-containing natural gas well were obtained and analyzed in this work. Results showed that H2S will gasify near wellhead during well killing when casing pressure decreases. To balance the bottom hole pressure, when H2S releases, the casing pressure increases as H2S content increases. As initial overflow volume increases, the annular temperature, annular pressure and the casing pressure increase significantly. When H2S gasifies, the casing pressure applied at wellhead should be higher at lower initial overflow volume to balance bottom hole pressure. In the well-killing process, the annular pressure and temperature decrease as drilling fluid density increases and a lower casing pressure is needed for balancing bottom hole pressure. The casing pressure is lower at a higher displacement for higher friction resistance. Besides, as well-killing displacement increases H2S will gasify at an earlier time. When drilling for H2S-containing natural gas well, early detection of gas kick should be more frequent to avoid severe overflow. Besides, higher displacement and density of drilling fluid should be considered to avoid stratum fracturing and prevent leakage accidents under the premise of meeting drilling requirements.

A Wellbore/Formation-Coupled Heat-Transfer Model in Deepwater Drilling and Its Application in the Prediction of Hydrate-Reservoir Dissociation

SPE Journal ◽  
2016 ◽  
Vol 22 (03) ◽  
pp. 756-766 ◽  
Author(s):  
Yonghai Gao ◽  
Baojiang Sun ◽  
Boyue Xu ◽  
Xingru Wu ◽  
Ye Chen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Drilling Fluid ◽  
Heat Transfer Process ◽  
Heat Transfer Model ◽  
Fluid Injection ◽  
Transfer Model ◽  
Hydrate Dissociation ◽  
Deepwater Drilling ◽  
Hydrate Reservoir

Summary On the basis of the wellbore and reservoir heat-transfer process during deepwater drilling, a heat-transfer model between wellbore and formation is built up for two different conditions: without riser and with riser. Wellbore and formation temperature distributions under different drilling-fluid-injection temperatures, flow rates, circulating times, and drilling depths are simulated by use of this model. Taking the hydrate-phase equilibrium into consideration, a possible region of hydrate-formation dissociation is analyzed, and effective methods are proposed to control the hydrate dissociation. The results indicate that, during shallow formation drilling, the increase of drilling-fluid flow rate will cause the wellbore temperature to rise, but below the hydrate-dissociation temperature in the whole process; during deep-formation drilling, drilling fluid is heated, and the heat is transferred from the deeper formation to the shallower formation through fluid circulation. Thus, the hydrate-reservoir temperature increases gradually along the wellbore radial direction. Hydrates will dissociate after the hydrate equilibrium temperature is reached; this may cause wellbore collapse or methane leak from the reservoir and result in disaster. To control hydrate dissociation during deepwater drilling, attention should be paid to the period of deep-formation drilling. Sensitivity studies indicate that the risk of hydrate dissociation rises as the drilling-fluid-injection temperature, flow rate, and circulating time increase.

scholarly journals Experimental Investigation On Hydrate Dissociation in Near-Wellbore Region Caused By Invasion of Drilling Fluid: Ultrasonic Measurement and Analysis

2021 ◽  
Author(s):  
Qingchao Li ◽  
Yuanfang Cheng ◽  
Ubedullah Ansari ◽  
Ying Han ◽  
Xiao Liu ◽  
...  
Keyword(s):  
Natural Gas ◽  
Marine Environment ◽  
Gas Hydrates ◽  
Drilling Fluid ◽  
Clean Energy ◽  
Hydrate Dissociation ◽  
Methane Leakage ◽  
Natural Gas Hydrates ◽  
Stabilizer Concentration ◽  
Hydrate Saturation

Abstract As we all know, development and utilization of clean energy is the only way for society to achieve sustainable development. Although natural gas hydrates is a new type of clean energy, uncontrollable hydrate dissociation and accompanying methane leakage in drilling operation threaten drilling safety and marine environment. However, dissociation range of natural gas hydrates around wellbore can't be reasonably and clearly determined in previous investigations, which may lead to the inaccurate estimation of borehole collapse and methane leakage. Then, the marine environment will be greatly damaged or affected. The purpose of the present work is to experimentally explore the dissociation characteristics of natural gas hydrates around wellbore in drilling operation, and analyze the influence law and mechanism of various factors on hydrate dissociation. It is expected to provide reference for exploring effective engineering measures to avoid the uncontrolled hydrate dissociation, borehole collapse and accompanying methane leakage. The experimental results demonstrate that acoustic velocity of hydrate-bearing sediment can be accurately expressed as quadratic polynomial of hydrate saturation, which is the theoretical basis for determination of hydrate saturation in subsequent experiments. Owing to the fact that hydrate dissociation is an endothermic reaction, hydrate dissociation gradually slows down in experiment. Throughout the experiment, the maximum dissociation rate at the beginning of the experiment is 8.69 times that at the end of the experiment. In addition, sensitivity analysis found that the increase of stabilizer concentration in drilling fluid can inhibit hydrate dissociation more than the increase in hydrate saturation. Hydrate dissociation was completely inhibited when the concentration of soybean lecithin exceeds 0.60wt%, but hydrate dissociation definitely occurs in the near-wellbore region no matter what hydrate saturation is. In this way, based on the requirements of drilling safety and environment protection, hydrate dissociation and accompanying methane leakage can be controlled by designing and adjusting the stabilizer concentration in drilling fluid.

scholarly journals Formation of a Low-Density Liquid Phase during the Dissociation of Gas Hydrates in Confined Environments

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 590
Author(s):  
Lihua Wan ◽  
Xiaoya Zang ◽  
Juan Fu ◽  
Xuebing Zhou ◽  
Jingsheng Lu ◽  
...  
Keyword(s):  
Natural Gas ◽  
Methane Hydrate ◽  
Phase State ◽  
Solid Phase ◽  
Potential Method ◽  
Methane Hydrates ◽  
Low Density ◽  
Hydrate Dissociation ◽  
State Of Water ◽  
Confined Environment

The large amounts of natural gas in a dense solid phase stored in the confined environment of porous materials have become a new, potential method for storing and transporting natural gas. However, there is no experimental evidence to accurately determine the phase state of water during nanoscale gas hydrate dissociation. The results on the dissociation behavior of methane hydrates confined in a nanosilica gel and the contained water phase state during hydrate dissociation at temperatures below the ice point and under atmospheric pressure are presented. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) were used to trace the dissociation of confined methane hydrate synthesized from pore water confined inside the nanosilica gel. The characterization of the confined methane hydrate was also analyzed by PXRD. It was found that the confined methane hydrates dissociated into ultra viscous low-density liquid water (LDL) and methane gas. The results showed that the mechanism of confined methane hydrate dissociation at temperatures below the ice point depended on the phase state of water during hydrate dissociation.

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