Actualizado: 22 de nov de 2020
Framed in beautiful settings and its people’s friendliness, the Kurdistan Region of Iraq offers a fascinating professional challenge and the possibility of developing an unique expertise and obtaining highly rewarding results in its world-class fields. By Mariana Olmeda.
It was 2012 and I was living in Buenos Aires when I got offered a job for projects in Kurdistan. Winds of change were blowing at that time and this exotic opportunity sounded just impossible to resist.
The Kurdistan Region of Iraq (KRI) is located in the North of the country and is recognized as an autonomous region in the current Iraqi Constitution (2005). Its overall population is slightly over 5 million and it comprises the governorates of Dohuk, Sulaymaniyah, Halabja and Erbil - this last one serving also as capital.
My first visit to Kurdistan, after a few months working in the projects from Europe, was as part of a geological field trip in the spring of 2013. I arrived there without a clear idea of what to expect and was rapidly blown away by the stunning, colourful landscapes. The spell was on. From that time onwards I returned to rig sites in the North, in the Dohuk Province, several times, to assist operations in my field. Each trip was unique, a new discovery, a new learning. Fifteen months after that initial field trip I was moving to Erbil with my 2 cats, Junior and Vito.
My experience as a resident was equally fascinating. The warmth of the people and all that history around, with the emblematic Citadel, dating from the 5th millennium BC, as the core of Erbil. Intense and exciting working days, ideal for those who enjoy operational settings and the related very dynamic and focused atmosphere. The possibility of being out in the fields and rigs in a few-hours car ride. The greenery, the always majestic Zagros mountains, the olive trees. The stops by the Dalal Bridge in Zakho (oldest open arch bridge in Middle East). The snowfalls in wintertime and that delicious rice pilaf with raisins and nuts. The daily 6.45 am van with the Premier League results or music as the usual main topics. And that unique feeling of community, of “oil family”, added to the equation.
That was my life in Kurdistan. And I so enjoyed it.
A bit of Geology & History
The Kurdish hydrocarbon fields are located along the Zagros fold belt, resulted from the collision of the Arabian and Eurasian tectonic plates. The degree of geological folding increases from low to high/thrust zone towards the North and East. A trend of NW-SE significant anticlines are present, mainly in the Central and Central-South areas, while the orientation becomes more WNW-ESE or even W-E in the Central-North and North of the Region. The reservoirs are carbonates (limestone and dolomite) of different ages, predominantly Cenozoic, Cretaceous, Jurassic and, in a minor proportion, Triassic. These reservoirs are in general exposed to high degree of faulting and fracturing of different types.
The geological complexity, in particular in the highly folded/thrust zone, which also constrains the seismic imaging, possess an interesting challenge to the subsurface evaluation and strategic well planning in these high-potential areas.
Figure 1: Location of Iraqi Kurdistan. Figure 2: Tectonic Map of Iraq, Jassim & Goff, 2006 (Color code: Light brown: Mesopotamian zone, Yellow: Foothill zone, Green: High Folded zone, Dark Brown: Imbricated zone, Light blue: Zagros Suture).
The first well drilled in Kurdistan, in the South-East of the Region, was Chia Surkh in 1901. The well proved oil shows and was abandoned. Only a few more wells were drilled in the years to follow, until the exploration well Baba Gurgur-1 in the Kirkuk Governorate, in 1927, resulted in the significant discovery of the Kirkuk Field (controlled by the Central Iraqi Government). From that moment, the oil activity experienced a significant increase in the region through the decades. By early 2015, there were 64 licenses delimited with 25 international oil companies (IOC) operating and 6,370 km2 of 3D seismic acquired (Mackertich & Samarrai, 2015). In 2019 a total of 160.3 MMbbls of oil produced in the KRI were exported via pipeline to Turkey (1), from where it is commercialized and shipped by sea to clients around the world.
(1) Source: Regional Council for Oil & Gas Affairs (RCOG) of KRG – Report prepared by Deloitte. 04/2020.
The Art of Developing Fractured Carbonate Reservoirs
Having worked for different reservoirs and fields in very different geological scenarios, I found my experience in North Kurdistan to be quite unique. Below are some key aspects and lessons learned with regards to subsurface well placement and design planning and overall reservoir development strategy, also linked to drilling, completion and surveillance activities.
As in any field, it is important to design a clear field development and reservoir surveillance strategy and to be able to incorporate lessons learned in the planning process. This statement becomes particularly relevant in fractured carbonates where events like pressure drops and water breakthroughs in the wells can occur and develop over shorter periods of time than other reservoirs, having a very high impact in the field’s production. Therefore, the development plan and production tactics should aim not only to optimise production but to delay the water breakthrough in the field as long as possible.
Horizontal wells and reservoir section placement in or going through highly faulted/fractured zones will have a significant impact in the production rates achieved. In water-free/early stages of the field life this may be very positive for hydrocarbon production, although its management may become challenging once the well has started producing water. Therefore, this should be factored-in and aligned with the overall field development strategy and its timings.
Minimising formation damage while drilling is very important to preserve as clean as possible the open tributary fractures that will act as conduit for the hydrocarbons to flow into the borehole. A careful planning of each well’s completion scheme to be able to isolate intervals and work per segments according to the needs (stimulation, fluid control/water production) has proven, in my experience, to be a must.
Once one or more wells in the field start experiencing water breakthrough, especially if it’s earlier than anticipated, it becomes key to understand how that water is related to existing producers and likely to affect other planned wells that may be part of the same fault or fracture system. This understanding becomes at this stage the key for the day-to-day well planning activities as the water rising through faults and fracture systems may be encountered several hundreds of meters above the field’s oil-water contact (OWC).
A detailed fracture mapping work combined with geological and petrophysical analysis, mud losses while drilling (if drilled overbalance), current production information (ideally per interval if completion is segmented; SSDs currently open or closed, PLTs if run) can help provide the best “present picture” of the field to continue the daily well planning and revise the overall field development strategy. This may be a complex task but also crucial in the identification and planning of infill, sidetrack and workover opportunities in advanced stages of the field evolution when the planning of long exposure, directional wells will become too risky due to water production and field pressure/production decline, greatly reducing the cost-benefit relationship of these wells.
Deeper areas (closer to the OWC) in less structured and fractured corridors must not be disregarded and may, in fact, represent good opportunities for a more stable well production and performance over time, despite probably lower initial production rates than those placed in more obviously fractured zones.
For the fields located in the thrust zone or close proximity to it, the areas where seismic imaging quality is very poor may still hold interesting opportunities worthwhile the risk. These opportunities can range from extending the existing development to unlocking new plays, so there is a clear appraisal element present in these cases. New water sources related to the footwall and its configuration is also a risk to be considered. The possible structural scenarios and associated risk assessment of each one should be carefully performed.
Back-to-back drilling and/or fast-paced, multi-rig, drilling campaigns constitute a big challenge especially in advanced stages of fractured carbonate field’s life, when water is already present and the subsurface targets are less obvious. In these cases, it is a must to gather all the expertise and work on defining, alongside the main well plans, the specific risk mitigation actions and contingency plans for each well and also an alternative drilling sequence that must be ready to be executed when necessary. The interdependency between planned wells must be established to set up the base case drilling scenario, followed by a continuous monitoring of the ongoing drilling as well as the behaviour of existing producers. This will allow to define the next steps as early as possible to avoid or minimise operational time loss.
About the Author
Mariana Olmeda is a Geophysical Engineer with a Postgraduate specialisation in Field Development, both from the University of Buenos Aires, UBA. She has worked in the development of diverse oil and gas fields of carbonate, clastic, volcaniclastic and tight reservoirs, participating in a variety of projects and basins of Argentina, Algeria, Peru, Bolivia and the Kurdistan Region of Iraq. She has been living in the Middle East since 2014.
She has a passion for sports, is an animal lover and a bass guitar player.
Picture taken in front of the Erbil Citadel, Kurdistan Region of Iraq, March 2015