Well Solutions for Improved Recovery

Program 3 addresses both classical single bore wells and more advanced well configurations in future field developments. These may include slender wells, branched wells, micro-field developments (a mother bore with permanent infrastructure installed also for future branches with instrumentation and flow control), and complex field development schemes.

Well integrity in the short-term, as well as the long-term, perspective is critical for safety and oil production. Methods for maintaining an overview and control will be given priority. Qualification and testing of zonal isolation will be included.

Well architecture can be a simple design with no or limited control and monitoring devices in the borehole, or the development can be based on maintenance-free, intelligent wells. Due to limited access and high costs, the recovery from subsea wells is normally lower compared to platform wells. To improve recovery, there is a need to make the well completions more intelligent, and/or to improve and develop new well completion designs and well service techniques.

Platform wells (dry wellheads) are easily accessible using low cost intervention systems. However also for platform wells there is a potential to improve the recovery with smart completions.

The purpose of using more complex well solutions is improved resource development through more effective reservoir management. Active control of injection and production of fluids is essential for optimised resource exploitation. As a consequence, reservoir uncertainties and flow control may be handled better with smart completions. The manipulation of the downhole valves can compensate for unfavourable downhole conditions such as early gas or water breakthrough.

Project summaries follows. Please see the annual reports for details.

Project 1: Slender well technology (2011-13)

Drilling costs represent more than 50% of total field development cost; hence a significant reduction of drilling costs will also have a major impact on the profitability of the field development.
Offshore wells that are being constructed to date have large well volumes and are drilled with large, high-cost drilling units. There is a significant potential for cost reduction by starting the well with a substantially smaller diameter, which implies reduced casing dimensions and costs, reduced mud volumes and costs, reduced Blow out Preventer (BOP) size and costs, in addition to the possibility of using lower-cost drilling units. The potential for cost reduction is greater for subsea wells and more significant with increasing water depths.
Project description and results
In this pre-project, the main focus has been on well construction. Reduced hole diameter allows higher pressure rating of well tubular and the well design may be based on an extensive use of liners. Liners may also simplify permanent plugging and abandonment (P&A) of the well. Expandable liner hangers, with an expansion cone remaining in place after setting, allow for relevant pressure rating. Enabling technologies like Managed Pressure Drilling (MPD) for control of Equivalent Circulation Density (ECD) and expandable casing/liner will allow for a reduced number of casing points and/or slimmer well completion. Centralization of casing/liner may cause restriction due to small radial clearances, and stepwise under-reaming may be applied to achieve proper cement bonding. The final hole size considered as minimum for both exploration and production wells is 5 7/8”. This allows full logging and coring capabilities and a standard 3 ½” drill string can be used. When reducing the diameter of the marine drilling riser to 13 ¾” (21” standard) and the BOP size to 13 5/8” (18 ¾” standard), the weight and riser volume will be reduced by approximately 45% and 55%, respectively.

Wellhead fatigue life will be increased using slender wells. Using a 13 ¾”  (12 ¾” ID) riser and a 13 5/8” BOP in 500 m water depth, initial simulations indicate that the mean and alternating loads on the wellhead are reduced by 30% and 40%, respectively.

Project manager: Sigbjørn Sangesland
Deputy: Jostein Sørbø

Project 2, Phase 1: Life cycle well integrity (2011-16)

During production, failure of well barriers may lead to leakages from the well. As a consequence, the well may be shut-in or abandoned, thereby causing significant production loss. Maintaining well integrity throughout the life-cycle of the well is therefore important in order to improve recovery.

Project objectives
The overall objective of the project is to ensure well integrity throughout the life-cycle of the well. An emphasis will be put on well barriers - to understand why well barriers fail, and also on well design - to understand how initial well design influences long-term well integrity.

Scope of work
Task 1: Start-up/initial activities (2011-12)
Task 2: Reliability of Downhole Safety Valves (2012-14)
Task 3: Thermal cycling of cement (2013-15)
Task 4: Cement-formation bonding (2013-14)
Task 5: Cement-casing bonding (2015)
Task 6: Assessment of cement sheath integrity (2016)
Task 7: Gas influx in cement (2016)

Project 2, Phase 2: Life cycle cement integrity (2016-19)

Cement sheaths are among the most important well barrier elements in the well, both during production and after well abandonment. It is however well-known that the integrity of the cement sheath can degrade significantly during normal production operations, such as shut-down/start-up, stimulations, workovers, etc., caused by the repeated temperature variations in the well. The casing expands and contracts due to temperature and pressure increases and reductions, which leads to formation of cracks and micro annuli (i.e. debonding) in the cement sheath, which may lead to sustained casing pressure and eventually potential failure of the cement sheath as well barrier element.

Furthermore, cement plugs are crucial for maintaining well integrity after P&A. However, there are several factors that influence the sealing ability of cement plugs, such as type of cement system, plug length, plug diameter and mud contamination, and the influence and importance of these factors are not completely understood.

It is important to understand how and why cement fails as well barrier elements, as such knowledge is important in order to prevent such failures. Also, such understanding can serve as input to specifying requirements for what acceptable barrier criteria for cement could be.

With respect to experimental studies of cement integrity, the current knowledge gaps can be summarized as follows:
  • There is insufficient information on the behaviour of the whole system; i.e. a well section consisting of real rock, cement and casing. The effect of mud is also unknown.
  • Previously used characterization techniques do not separate between debonding and the formation of cracks in cement. I.e. it is unknown whether the observed loss of zonal isolation is caused by debonding of cement (towards the casing and/or formation, by cracks in the cement sheath, or by both debonding and crack formation.
  • It is unknown what micro annuli and cracks in cement actually look like, and how different fluids flow through these leak paths.

The objective of this project is to study the sealing ability of cement throughout the life-cycle of the well, including after well abandonment.

The intention is to perform qualitative good research where the results can give input on which parameters and well conditions that influence cement integrity, with respect to cracking/debonding of the cement and subsequent leak rates through the cement barrier element.

Project manager: Torbjørn Vrålstad
Deputy: Jostein Sørbø

Project 3: Improved Plugging & Abandonment (P&A) (2011-16)

Thousands of wells need to be plugged and abandoned at the NCS in the next few decades, and this will be both time-consuming and very costly. As most plug and abandonment (P&A) operations currently require a drilling rig, it is important to find less time-consuming and more cost-effective methods, since these drilling rigs instead should be used to drill new wells and thereby improving recovery.

Project objective
The overall objective is to make P&A operations more cost-effective while maintaining or improving well integrity. There are several important problem areas within P&A. For this project, two main topics have so far been selected; permanent plugging materials and P&A of subsea wells.

Scope of work
Task 1: Start-up/initial activities (2011-12)
Task 2: Geopolymers as potential plugging  materials (2012-16)
Task 3: Long-term integrity of plugging materials (2013-16)
Task 4: Cost and time estimation of subsea multi-well P&A campaigns (2013-15)
Task 5: Tubing left in hole (2013-15)

Project manager: Torbjørn Vrålstad
Deputy: Jostein Sørbø

Project 4: Production Optimisation through the use of Water Shut-offs (2011-16)

Motivation & Background
Well production optimization and reservoir management requires an in-depth evaluation and understanding of field geology, wells’ operational conditions and restrictions, coupled with surface facilities capabilities. This enables accurate predictions, effective control, and efficient management of both injected and produced well fluids. 

Injected fluids (water, chemicals, gas, etc.) should be efficiently utilized to displace formation oil, whereas produced fluid composition should be optimized with respect to quantity and quality of unwanted (water and/or free-gas) fluids. In addition, produced formation fluids, such as water and free-gas, will require separation and possibly reinjection (either one or both water or gas) for pressure maintenance, lack of or reduced disposal capabilities, lack of pipeline for gas transportation to the market, etc. For example, production of water increases with the well’s life-time leading to increased lifting and handling problems (and costs), inefficient utilization of the reservoir’s energy, and ineffective sweep of the oil-bearing formation.

Traditional industry-used technologies to combat the production of water include well intervention solutions such as mechanical ones deployed in the wellbore (e.g., patch flex, downhole oil/water separation and subsequent injection into a water zone) or chemical ones used as shallow- or deep-placement of gels or foams, cement squeeze, and Disproportional Permeability Reduction (DPR) systems. The utilization of the appropriate and most effective solution requires (a) the understanding the source of the unwanted fluids (e.g., watered-out layer, natural fractures, flow behind casing, coning), (b) the existence of a tuned reservoir model, (c) design of a customized solution based on the field/well operational constrains, (d) deployment of carefully designed well solution, (e) post-job well monitoring, and (f) evaluation of solution’s effectiveness.
Project Objectives
This project aims at addressing the management of unwanted water produced along with oil through a cost-effective, well-customized, environmentally-friendly well solutions.

The project specific objectives are as follows:
  • Evaluate current mechanical and chemical solutions for water shutoffs
  • Evaluate current technology for production profile modification through the use of Disproportional Permeability Reduction (DPR) systems
  • Evaluate use of chemicals for a more effective and efficient management of water production
  • Develop new or improved screening, methodologies, data requirements, processes and workflows for selecting appropriate customized well solutions
  • Apply new technologies to field pilots

Project manager: Dimitrios Hatzignatiou 
Deputy: Jan David Ytrehus
Project 5: Technologies for barrier evaluation and P&A (2016-19)

The overall motivation for this project is the need to introduce lower cost well P&A solutions.

When designing a P&A operation the sealing quality of the cemented casing (or other annular material) must be assessed. Borehole cement evaluation logs are primarily used for this purpose and aim to establish the height of the cement, the bond quality to the casing and formation and identify any defects that might impact the quality of the annular seal such as channels or voids. However current technology has its limitations and knowledge gaps include:
  • The relationship between the sealing quality of a cement barrier barrier and the log interpretation result is not quantifiably defined but typically based on a “rule of thumb”.
  • The cement evaluation log is not an annular seal log, a cement barrier approved by testing can appear poor on a cement log and vice versa.
  • log interpretation is often qualitative rather than quantitative and results vary by service provider, logging engineer, interpreting engineer.
  • Annular seal evaluation through multiple casing strings is a challenge for current technology.The well abandonment process requires that a barrier be established that permanently seals the well.
Develop methods to quantify the quality of alternative well P&A solutions by:
Investigating the link between cement evaluation techniques and the actual sealing quality of the well barrier
Investigating the feasibility of emerging P&A concepts 

Project manager: David Gardner
Deputy: Torbjørn Vrålstad

Project 6: Cementing Irregular Wellbore Geometries (2015-18)
Knowledge needs
The primary cementing of casing is among the most critical elements of a well. This is true not only for the well construction, but for the entire life cycle of a well. The quality of a cementing job is critical in several aspects:
  • Zonal isolation during drilling and production
  • Well control barrier
  • Protection of the casing from formation fluids
Since the Macondo incident, the primary cementing jobs are even more in focus. “Using cement as a viable barrier to protect the wellbore from dangerous influxes of water or gas looms
as one of the biggest issues facing the industry as it looks ahead 20 years and beyond”; Katie Mazerov, contributing editor, Drilling Contractor, March 2013. The planning of a cementing job is mostly guided by a 1 D numerical simulation of the cementing job focusing on the resulting pressure profile along the wellbore and simplified assessment of the displacement processes. This planning process is limited in detail and does not take into account the 3D calliper, and it is hardly ever verified because it is impossible to evaluate the quality of the cementing job.

In reality, a large number of factors influence the result of a cementing job:
  • The state of the fluid in the wellbore prior to cementing (mud pockets, filter cake, …)
  • The rheology and density of the spacer and slurries
  • The temperature and pressure in the well bore
  • The calliper and stability of the wellbore
  • The eccentricity of the casing
Decisions related to the planning of cementing operations today suffer from shortcomings: (i) There is a lack of high quality experimental results from cementing of realistic geometries which can be used for evaluation of work processes for planning cementing jobs; (ii) 3D numerical modelling tools for evaluation of cementing job designs are not qualified for realistic wellbore geometries and available to a wide range of users; (iii) There is a lack of understanding of one of the most critical operations in the oil and gas industry.

In order to achieve a higher reliability in planning and running of cementing operations we need (i) improved understanding of the transients in the displacement process when cementing in irregular wellbores and (ii) improved understanding of the effect of wellbore irregularity on the quality of the primary cement job.

In order to reach these goals, we need to improve and develop: (i) Experimental methods for generating dynamic high-resolution data. (ii) Mathematical methods for detailed modelling of the cementing process.

The same mathematical methods, or simplified versions of these, may subsequently be applied for planning and management of the primary cementing process, in order to reach the goal of a more reliable primary cement job.
The primary objective of this project is to develop a methodology for planning cementing operations of wellbores with irregular geometries. To achieve this, we plan to address the following secondary objectives:

Improved experimental knowledge basis: develop a unique physical experimental setup for 3D printing of irregular wellbores based on 3D calliper logs and perform cementing experiments with these,

Improved 3D numerical modelling: develop and asses methodology for 3D numerical modelling of the displacement process during cementing using open software code and general commercially available software framework. The immediate result of this project will be better methods for planning of cementing jobs in irregular wellbore geometries. The long-term results will be more efficient cementing operations and improved zonal isolation contributing to improved recovery and well integrity.
Project manager: Hans Joakim Skadsem
Deputy: Jan David Ytrehus

Project 7: Leakage risk assessment for plugged and abandoned oil & gas wells (2016-19)

Knowledge needs
After more than 40 years of oil & gas production on the Norwegian Continental Shelf (NCS), a large number of wells will have to be plugged and abandoned (P&A) due to low production or technical failures. According to a recent article in Teknisk Ukeblad and information provided by the Norwegian Oil & Gas Association, there are more than 3000 wells to be plugged and abandoned on the Norwegian Continental Shelf in the next 30-40 years, the accumulated cost being in the range 400-500 billion NOK.

 From the oil & gas operators’ and Norwegian authorities’ perspective, there are two main success criteria with respect to the “properties” of a plugged and abandoned well; i) the well shall not leak in an “eternal” perspective and ii) the costs of plugging and abandoning the well should be as low as possible.

P&A well design performed on the NCS today follows a best practice approach. This means that the selected P&A solution either adheres to NORSOK D-010 or even stricter company standards set by the different operators. While such an approach may give satisfactory results in terms of the first success criterion above, it does not help the industry improve with respect to reducing the cost. In order to combine and possibly trade-off the two success criteria, there is a need for a methodology that can quantify the quality of a given P&A solution. A quality measure that is easy to communicate and that can be quantified is the risk of leakage from a given P&A design, i.e. the probability that a leak will occur and the corresponding leakage rate. With such a methodology, any proposed P&A solution will have a measure of quality attached to it, which is a good starting point for evaluating cost-benefit ratios, and to evaluate new barrier element technologies such as for example.

The driver for this project is the need to implement a methodology that allows a P&A planning team to quantify the quality of alternative P&A well designs by estimating the leakage risk. We believe this will pave the way for more efficient P&A designs and contribute to faster qualification of new barrier technologies for P&A. The main research questions that need to be addressed in order to achieve this are:
  • What is the status of the well barrier elements at the end of its operational lifetime, i.e. prior to the well being plugged and abandoned?
  • What will happen in the area around a plugged and abandoned well in a short- and long-term perspective?
  • What is the lifetime of the well barrier system in a plugged and abandoned well?
  • If the P&A well barrier system fails, what are the consequences in terms of leakage rates and volumes?

The primary objective of this project is to develop a methodology for evaluating the quality of the barrier system of a permanently plugged and abandoned well by expressing the quality of the barrier system in terms of leakage probability and potential future leakage rates.
Secondary objectives
  • Establish a reliability model for the barrier system in a permanently plugged and abandoned well.
  • Develop a leakage calculator for oil & gas escaping the barrier system.
  • Develop a model for long- and short-term pressure forecasting in the well vicinity.
  • Establish uncertainty quantification models for all phenomenological models.
  • Developed and implement sensitivity analyses to understand critical factors.
  • Validate the applicability of the methodology on two real cases.
  • Develop a software (prototype) tool that integrates all models and input data.
  • Educate a Post-Doctoral fellow in the field of P&A barrier analysis and associated risk and uncertainty modelling.
The final outcome will consist of a set of data, interlinked models and calculators that are integrated in a software prototype tool. It will be developed in close cooperation with several operators on the NCS, the ambition being to have a prototype that can be tested in the planning phase of P&A operations at the end of the project.
Project manager: Øystein Arild
Deputy: Torbjørn Vrålstad


Torbjørn Vrålstad

Jostein Sørbø

Sigbjørn Sangesland

Jan David Ytrehus

Hans Joakim Skadsem
David Gardner
Øystein Arild