Study on Wellbore Temperature and Pressure Distribution in Process of Gas Hydrate Mined by Polymer Additive CO₂ Jet

Abstract

In order to solve the problem of hydrate reservoir collapse and hydrate regenerated in the process of solid fluidization of natural gas hydrate, a new method of natural gas hydrate exploit by high‐polymer additive (low viscosity carboxymethyl cellulose LV‐CMC) carbon dioxide jet was proposed. The wellbore temperature and pressure changes during this process are analyzed, and the wellbore temperature and pressure model are established and solved by the state space method. This paper also analyzed the effects of relevant parameters on hydrate decomposition, such as injection flow, temperature, and pressure. The results show that increasing the injection pressure allows the hydrate decomposition site to be closer to the annulus outlet. Compared with water, with polymer additive CO2 fluid as the drilling fluid, the intersection point of phase equilibrium curve and annular pressure curve is closer to annular outlet, which is obviously more conducive to well control. In order to avoid phase changes, the injection pressure of the carbon dioxide fluid of the high‐polymer additive should not be lower than 10 MPa, and the injection temperature should not be higher than 285 K.

Transient Temperature Distribution of Underground Carbon Dioxide Salt Cavern Storage With State Space Model

“…Figure 1 shows the phase change of CO 2 , when CO 2 approaches the supercritical state (31.1 • C, 7.38 MPa), which is likely to occur somewhere along the wellbore and in the salt cavern (Li et al, 2017;Wei et al, 2020).…”

“…Carbon capture and storage (CCS) is a technique of lower carbon utilization for fossil fuels on a large scale (Li et al, 2015). This technique was developed in the 1970s and has been used in enhanced oil recovery with CO 2 (CO 2 -EOR), in enhanced geothermal systems with CO 2 (CO 2 -EGS), CO 2 storage with gas recovery (CO 2 -EGR), and CO 2 storage with saline water recovery (CO 2 -EWR) (Wang et al, 2012;Sun et al, 2013;Boot-Handford et al, 2014;Li et al, 2014;Luo et al, 2014;Middleton et al, 2015;Wei et al, 2020). In recent years, a group of underground salt cavern storages with various advantages have been built in China (Zhang and Goh, 2012).…”

“…Studies on wellbore temperature distribution have been conducted since the 1950s. Both numerical and analytical approaches have been adopted to estimate the wellbore temperature (Hasan and Kabir, 1996;Wei et al, 2020). The earliest study of wellbore temperature was by Ramey.…”

“…The earliest study of wellbore temperature was by Ramey. He drew charts for predicting bottom-hole circulating temperatures (Ramey, 1962;Wei et al, 2020) and proposed a steadystate model for obtaining the hole wellbore temperature distribution, which could not be applied to transient behavior (Hasan and Kabir, 2002;Yang et al, 2017;Wei et al, 2020). Raymond proposed the first numerical model for predicting temperature distributions for both transient and pseudo-steadystate conditions (Raymond, 1969).…”

“…For CO 2 injection, the flow and thermal behavior in the wellbore involves some unique characteristics. Many researchers also developed CO 2 two-phase flow models under isothermal conditions (Wang et al, 2011a,b;Guo and Zeng, 2015;Li et al, 2016;Wei et al, 2020). Although using a salt cavern for CO 2 storage is not equal to injecting CO 2 into the wellbore.…”