An Abnormally High Pressure Zone have been detected to be the Culprit Of Many Well Integrity Issues in Dukhan Khuff Wells.
Authors: Sultan Ahmed A. 
Published: May 2016

An abnormally high pressure formation caused the loss of a number of Dukhan Khuff Gas (DKG) wells. The Sudair formation has always been considered normally pressured throughout the Dukhan Khuff gas field area. However, this case study supports the author's hypothesis that, contrary to that belief, Sudair can be abnormally pressured.

Two DKG wells A and B were the subject of this case study. These wells experienced loss of integrity due to high annuli pressures and were recently worked over. The author's abnormally high pressure zone hypothesis is based on actual real data from both of these wells.

DKG wells were drilled more than thirty years ago. All 28 wells were drilled through the Sudair formation without any pressure or well control issues. However, at some point in time, most of these wells developed annulus pressure in one or more of their annuli. How did that happen? To answer this question, the author searched other operator's experiences in the area. The search pointed out that the Sudair formation is not always normally pressured; it can also be abnormally pressured. We have seen reports of Sudair high formation pressure associated with high rate salt water flow, high rate gas flow and in occasions very low rate salt water flow. While the high rate flows are detectable, it's the very low rate high pressure salt water flow that is almost impossible to detect. Another finding is that the Sudair formation pressures are neither equal nor uniform over a large area but rather different and localized.

What could we have done differently thirty-five years ago? The answer is simply no thing because we did not have the knowledge and knowhow of today. However, there are lessons to be learnt, t's to be crossed and i's to be dotted.

Introduction

Dukhan Khuff is a non associated high pressure gas reservoir. The field was developed in the late 1970s to supply fuel gas to the power generation plants. Because of the high pressure, Khuff Gas wells were designed and constructed according to the highest applicable standard at the time. However, most of these wells developed annulus pressure in one or more of their annuli.

DKG wells crossed a number of oil and gas bearing formations that made it almost impossible to finger print the effluents that are flowing from the different annuli. Also, the experienced annuli pressures were, in most cases, within the normal range. Hence, the source of the annuli pressures remained a mystery.

The occurrence of a very high sustainable tubing casing annulus (TCA) pressure in DKG-well A prompted us to search for the source of the noted unusual high pressure. Events from the well history as well as pressure data obtained during its workover supports our belief that an abnormally high pressure formation was the cause of the experienced high annulus pressure. While the exact formation bearing the high pressure had not yet been identified its properties and characteristics have become partially known.

Our second case study DKG-well B is a recently drilled well. As a result of high annulus pressure, the well developed integrity issues immediately after it was put on production. During the workover to reinstate the well's integrity it became clear that the Sudair formation is the likely source of the high annulus pressure.

This case study is a summary of the events that led to the discovery of the culprit high pressure zone.

What's next? Now that we know what has caused the loss of integrity of a number of DKG wells. What we present here are other operators' experiences with Sudair formation and what have they done to predict and overcome its pressure.