English abstract
Halite precipitation and liquid loading are considered as perilous threats to gas wells
impacting their productivity at the end of the wells' production lifetime. Accurate
prediction of the start of these problems is very essential to guarantee a proper mitigating
or managing plans. Predicting liquid loading problem is very mature and this issue is
proved to be managed by reducing the size of the tubing (i.e. installing velocity string
(VS)). In contrast, the prediction of the onset of halite precipitation is still lacking
sufficient research and the existing approaches are only applicable in well level and yet
not adequately validated. Additionally, the current deployed halite management measures
are inefficient and not cost effective. There are many gas wells in PDO company suffering
from halite precipitation, and various actions have been taken to mitigate and manage this
problem. A more recently identified possibility is utilizing smaller completion size
(velocity string) to mitigate / remove halite problem, which at the same time comes with
benefit of gas well deliquification. However, more study is required to confirm the
suitability and efficiency of this possible solution. This study aims to develop a general
and replicable model, using halite envelope, to predict the halite precipitation issue in a
gas field in Oman. To achieve this objective, thirty halite envelopes for thirty different gas
wells, known to have experienced halite precipitation problem, were simulated. The
simulation showed that, there is significant variation in the size and shape of the halite
envelope of the different wells and therefore the concept of constructing a single envelope
for the whole field turned out to be infeasible. However, grouping halite envelopes of
different wells based on their inflow resistance, followed by constructing a halite envelope
model for each group was proved to be a powerful tool for halite prediction. The study
also investigated the technical viability and the pros and cons of using velocity string
technology as a new approach in managing halite precipitation issue. This was achieved
by simulating the halite envelope of few wells assuming different sizes of velocity string
are installed, followed by analyzing the halite envelopes and estimating the timing of
halite precipitation re-occurrence. The study revealed that using velocity string as a halite
remedial technique depends mainly on the rock quality as well as the time of installing the
velocity string. Furthermore, the study aims to predict the time of the liquid loading issue
of same wells, evaluating the impact of installing velocity string on liquid loading and
assess the synergy between halite management and de-liquification by using velocity
string. This objective was achieved by estimating the time it takes the selected wells to
load-up and then compare the time to liquid loading with the time of halite recurrence
when velocity string is installed. The study concluded that generating a synergy between
halite management and de-liquefaction using velocity string depends mainly on the rock
quality and the size of the installed VS.
