Near Wellbore Salt Precipitation in Gas Reservoirs

Near Wellbore Salt Precipitation in Gas Reservoirs

Nair, R.

Zitha, P.L.J. (mentor)
Egberts, P.J.P. (mentor)

Civil Engineering and Geosciences

Geoscience & Engineering

Petroleum Engineering

2015-09-25

Production wells in gas reservoirs often experience rapid production decline towards the late production stage. In many cases, this behavior can be attributed to salt precipitation in the near wellbore region. Water evaporates in the vicinity of the well bore with pressure drop, leading to an increase in the dissolved salt concentration, causing salt precipitation when the solubility limit is exceeded. Salt deposition causes the blockage of gas flow in the vicinity of the wellbore and increases towards the end of lifetime of a gas field, thus becoming problematic for most North Sea assets. Regular downhole fresh water treatments are required to restore the production back to normal. However, these water treatments are expensive and are required quite frequently. Thus, a better understanding of this phenomenon and the conditions under which it takes place is necessary. Additionally, the question arises whether there exists a better reservoir management strategy that can can improve control over well productivity. The model used to model salt precipitation in this work is a compositional two-phase N- component porous media flow model under isothermal conditions(2pNcmin) developed in the numerical simulator DuMuX. A sensitivity analysis was carried out to measure the sensitivity of the model to certain critical parameters and to understand the phenomenon better. The concept of a drying-transport balance was then developed, which can help understand the salt precipitation trends occurring under differing conditions. A study of the variables controlling the productivity of wells plagued by salt precipitation shows that there does exist an optimized reservoir management strategy which can better the cash flow from such wells. Based on these results, a simplified analytical model was developed to show the scope for optimization. Furthermore, an optimization problem was formulated to maximize the Net Present Value (NPV) of wells undergoing cyclic production and water washing.

salt
precipitation
gas

http://resolver.tudelft.nl/uuid:35b05f90-1ecf-4015-a514-18efb648be49

2015-12-25

Student theses

master thesis

(c) 2015 Nair, R.