Comprehensive Wax Evaluation of High Wax Content Crude of A100 Field; From Lab Characterization to Prevention and Mitigation Measures
Authors: Belashehr Turia. , Essa Fathi. , Attia Alsiddiek. Alaboub. , Sherik. Ayoub. 
Published: October 2023

At Onshore (area A) Oil Field in Libya, most wells have experienced wax deposition in the tubing string at different stages of Wells life which caused a significant production drop. The purpose of this research is to identify the root cause of the recent wax appearance, control and prevent wax deposition in the tubing string. Multiple sensitivity analysis revealed potential Reservoir and Completion remedies to prevent and control Wax deposition in the field.

Three candidates Wells (W1, W2 and W3) suffering from wax deposition were selected for this study, the three wells represent all possible PVT regions/Blocks in the field and exhibit different Wax developments. Representative liquid PVT samples were collected and analyzed at the lab to determine full Wax properties such as Wax Appearance Temperature, Wax Content etc. Then a comprehensive fluid characterization was performed in a PVT application which involved; Equation of State modelling, fine-tuning EOS to wax and original reservoir fluid experimental data. The final fine-tuned phase behavior along with wax precipitation curve were then incorporated in both steady and unsteady state simulators. The Steady state simulator was used to perform precipitation modelling which determines preliminary at what depth and in which condition wax precipitation occurs, on the other hand, The Unsteady state application was used to perform severity modelling which determines preliminary the thickness of Wax and the expected cycle between each Wax removal job. Most Recent production data were used to fine tune both steady and unsteady state simulator and to be used to perform sensitivity analysis on main factors affecting Wax development and their impact on wax precipitation and severity such as flow rates, wellhead pressure, GOR, Productivity Index, Water Cut.

Wax appearance temperature (WAT) of the three samples were found to be in the range of 53 - 61°C and wax content was found to be in the range of 24-26% which indicated that the reservoir fluid is highly waxy in nature. Moreover, the fluid characterization along with most recent pressure surveys indicated that the field pressure in the past years has fell below saturation pressure which also triggered wax deposition as light component leaving the heavy paraffinic components inside the reservoirs. Many Sensitivity scenarios have been conducted on flowrates, productivity index, wellhead pressure, Water Cut, etc. suggesting that the Wells have low reservoir quality – Low Permeability – or get severely damaged along the way – low productivity Index – tends to be suffering more from Wax deposition as the low rate creates cooler tubing condition – Below 53 -61 °C –at around 2000ft – 4000ft where wax starts to deposits. The sensitivity analysis suggests potential reservoir and completion remedies to prevent and control Wax deposition such as reservoir stimulation, pressure maintenance, Artificial Lift System & Tubing heaters.

It is a comprehensive evaluation was performed on multiple wells to examine the wax appearance phenomenon in the field, the study was entirely based on experimental data and actual production data which revealed the root cause of wax deposition, potential and practical reservoir level and completion level solutions to control and prevent Wax deposition.