The Khazzan field lies in a remote desert area around 350km south-west of Muscat and gas was first discovered there during the 1990s (in fact at Makarem-1 in 1994). Locating the whereabouts of the gas was one task, however understanding it properly – getting an accurate picture of its extent and character, as well as finding the best way to produce it from the dense, hard rocks that contain it – was a completely different type of challenge and one that called for specialised expertise.
It was with this critical objective in mind that the international oil company, BP, was invited to deploy its industry-leading exploration, reservoir development and drilling & stimulation expertise. In 2007, the company signed an appraisal and development agreement with the Ministry of Oil and Gas in Oman- and the work that will ultimately result in the delivery of gas from the Khazzan field, began.
The first task was to create a detailed three-dimensional model of the subsurface. Given the remote location, the vast size of the field and the fact that the gas was located at depths of several kilometres, this was to be a considerable challenge. As an industry-leader in 3D seismic acquisition, processing and interpretation, BP planned to use proprietary sonar scanning technologies to find out where the reservoirs were; how deep and wide they were estimated to be; what quality of gas was projected; what the rocks were like and how easy would it be to get out.
What was then the largest-ever onshore 3D seismic survey was carried out in 2008. A fleet of specialised trucks criss-crossed the field – an area much bigger than the size of Greater London – taking thousands of soundings using seismic vibrators, mounted on the back of the trucks. These sent sound waves deep into the subsurface which were reflected backby the structures, rocks and reservoirs beneath. A total of 2,800 square kilometres was mapped using this technology, with many gigabytes of data being collected at 12km intervals across the field.
Interpreting the captured data and building a computerised 3D model of the reservoirs requires real skill and expertise, and the BP Khazzan Reservoir Development team — now numbering around 40, about 60 per cent of whom are Omani nationals — had the task of doing just that. Their aim is to understand the size, volumes, risks and challenges, as well as what resources would be needed to produce the gas – and where best to drill.
The survey confirmed a significant potential for recoverable natural gas within the reservoirs, lying at varying depths up to 5 kilometres. It also revealed a number of likely challenges in getting that gas out. The density, hardness and temperatures of the Khazzan rocks were found to be much greater than normal, with implications for the design and specification for the wells required to produce the gas. The quality and accessibility of the gas in each reservoir was also different.
The 3D model built by the team has an incredible level of detail and is continuously used to select well locations, decide the type of well to be drilled and ultimately to guide the full field development planning. As Abdullah Al Anboori, New Well Delivery Team Leader, comments: “Nine years ago, the Khazzan seismic survey was shot over a flat desert using BP’s latest technology which was ‘the world’s fastest technique’. It was the first trial of its kind in the world and broke a new world record for land seismic acquisition productivity, a big achievement. Now, I am using this seismic to locate and plan our new wells: it has fundamentally changed the field development from pattern drilling to seismic-driven targeted drilling.”
Understanding the gas and the reservoirs beneath Khazzan did not stop at the initial survey and 3D modelling. The interpretation and integration of data continues to this day, building an ever-more detailed picture of the subsurface that aids the ongoing drilling programme.
New software has been developed that enables various departments at BP Oman to understand the complexities of the field at the click of a mouse. The ‘Siraaj’ computer application was developed specially for Khazzan and brings together a number of datasets and information to show different aspects of the reservoir and field development activities in one place. It shows when and what type of well will be best to drill, indicates the impact that this will have on the pipeline system and overall production. As a single tool instead of many, Siraaj reduces time and improves efficiency among the BP Oman’s teams.
As Ghaleb Al Habsi, a Reservoir Engineer in Reservoir Management says: “With its user-friendly interface, Siraaj provides a quick and easy answer to a multitude of complex business problems related to the field development plans. The tool allows me to interact with different disciplines to see the bigger picture of the field development activities in a very graphical and interactive manner; and best of all, a lot questions associated to well type, spacing, drilling sequence, etc., can now be answered within minutes.”
Having developed a detailed reservoir description and proper estimation of the recoverable resources (gas), the next challenge was how to build the infrastructure to safely and efficiently produce gas. At latest stage of construction, Khazzan’s first gas is due end of 2017.