Worlds First Offshore Horizontal Well Using Jointed Pipe Cemented Frac Sleeve Technology

The Valdemar field, located in the Danish sector of the North Sea, targets a Lower Cretaceous, "dirty chalk" reservoir characterized by low permeabilities of <0.5mD, high porosities of >20% and contains up to 25% insoluble fines. To produce economically the reservoir must be stimulated. Typically, this is by means of hydraulic fracturing. A traditional propped fracture consists of 500,000 to 1,000,000 lbs of 20/40 sand, placed using a crosslinked seawater-based borate fluid. The existing wells in the field are completed using the PSI (perforate, isolate, stimulate)1 system. This system was developed in the late 1980s as a way of improving completion times allowing each interval to be perforated, stimulated and isolated in a single trip and has been used extensively in the Danish North Sea in a variety of fields. The system consists of multiset packers with sliding sleeves and typically takes 2-3 days between the start of one fracture to the next. Future developments in this area now require a new, novel and more efficient approach owing to new target reservoir being of a thinner and poorer quality. In order for these new developments to be economical an approach was required to allow for longer wells to be drilled and completed allowing better reservoir connectivity whilst at the same time reducing the completion time, and therefore rig time and overall cost. A project team was put together to develop a system that could be used in an offshore environment that would satisfy the above criteria, allowing wells to be drilled out to 21,000ft and beyond in excess of coiled tubing reach. The technology developed consists of cemented frac sleeves, operated with jointed pipe, allowing multiple zones to be stimulated in one trip, as well as utilizing a modified BHA that allows for the treatments to take place through the tubing, bringing numerous benefits. The following paper details the reasons for developing the new technology, the development process itself, the challenges that had to be overcome and a case history on the execution of the first job of its kind in the North Sea, in which over 7MM lbs of sand was pumped successfully, as well as the post treatment operations which included a proof of concept in utilizing a tractor to manipulate the sleeves. Finally, the production performance will be discussed supported by the use of tracer subs at each of the zones.

Modified Carbon Dots with Lowered Retention and Improved Colloidal Stability for Application in Harsh Reservoir Condition

Tracer technology has been increasingly used in inter-well tests to investigate reservoir performance, reservoir connectivity and residual oil saturation for providing useful information to improve decision making in reservoir management. Stable nanoparticle tracers with high-sensitive real-time detectability are highly desired, and as one of the nanoparticles tracers, carbon dots (C-dots) have been studied and tested as nano-agent tracer in field trial for reservoir monitoring. In this research, we report a modified method to synthesize fluorescent C-dots and fluorinated, sulfonated or zwitterionic functional groups were incoprtated into the C-dots. The synthesis reaction occurs at hydrothermal conditions with inexpensive starting materials and is readily to scale up for industrial application. Optical properties of the synthesized colloidal C-dots were studied by UV-visible and fluorescence spectroscopies. Colloidal stability was studied by dynamic light scattering (DLS) measurements, and retention of the C-dots in porous medium was evaluated by adsorption experiment with limestone rock. The synthesized C-dots are readily dispersible in freshwater and synthetic brines and exhibit improved colloidal stability in hot brine and lowered retention in reservoir rocks. In comparison with those C-dots reported in literatures, our results suggest that the synthesized C-dots using the modified procedure have excellent fluorescence properties, improved thermal stability, photostability, and water dispersibility, enabling their use as optically detectable nano-agent tracer in oil field application.

Waterflood Analysis in Compartmentalised Reservoir Using Multiwell Retrospective Testing and Tracers

The study field consists of four oil pays and is currently going through a waterflood trial. Due to a presence of high amplitude faulting it becomes crucially important to understand the geology of the field and reservoir connectivity prior to progressing the waterflood project. The results of the cross-well tracers have indication (some strong and some vague) of communication between a trial water injector and all oil producers in the same and adjacent compartment. Since the wells were equipped with permanent downhole pressure gauges it was possible to decipher the cross-well communication using the Multiwell Retrospective Testing (MRT) technique based on multiwell deconvolution algorithm (MDCV). The results of MRT study were showing no traceable communication between trial water injector and offset wells in adjacent compartment except one producer which showed a strong response across the fault. By correlating the MRT results with seismic profile and well completion it became possible to establish how exactly the main pay is communicating between the compartments. It also carried few learning points on how to interpret results of cross-well tracers and MRT in terms of reservoir properties.

Adaptive Prediction of Enhanced Oil Recovery by N2 huff-n-puff in Fractured-Cavity Reservoir Using an FNN-FDS Hybrid Model

N2 huff-n-puff has proven to be a promising technique to further improve oil recovery in naturally fractured-cavity carbonate reservoirs. The effect of enhanced oil recovery (EOR) by N2 huff-n-puff is significantly affected by various dynamic and static factors such as type of reservoir space, reservoir connectivity, water influx, operational parameters, and so on, typically leading to a significant increase in oil production. To reduce the prediction uncertainty of EOR performance by N2 huff-n-puff, an adaptive hybrid model was proposed based on the fundamental principles of fuzzy neural network (FNN) and fractional differential simulation (FDS); a detailed prediction process of the hybrid model was also illustrated. The accuracy of the proposed FNN-FDS hybrid model was validated using production history of N2 huff-n-puff in a typical fractured-cavity carbonate reservoir. The proposed model was also employed to predict the EOR performance by N2 huff-n-puff in a naturally fractured-cavity carbonate reservoir. The methodology can serve as an effective tool to optimize developmental design schemes when using N2 huff-n-puff to tap more remaining oil in similar types of carbonate reservoirs.

Asphaltenes: Fundamental Principles to Oilfield Applications

The sophisticated molecular imaging methods, atomic force microscopy (AFM) and scanning tunneling microscopy (STM), have been utilized to image individual asphaltene molecules, both their atoms and bonds, and their electronic structure. The stunning images have confirmed previous results and have all but resolved the long-standing uncertainties regarding asphaltene molecular architecture. Asphaltenes are also known to have a strong propensity to aggregate. The dominante asphaltene molecular structure and hierarchical nanocolloidal structures have been resolved and codified in the Yen-Mullins model. Use of this model in a simple polymer solution theory has given the first equation of state (EoS) for asphaltene gradients in oilfield reservoirs, the Flory-Huggins-Zuo EoS. With this EoS it is now possible to address reservoir connectivity in new ways; equilibrated asphaltenes imply reservoir connectivity. For reservoirs with disequilibrium of contained fluids, there is often a fluid process occurring in geologic time that precludes equilibrium. The collection of processes leading to equilibrium and those that preclude equilibrium constitute a new technical discipline, reservoir fluid geodynamics (RFG). Several reservoirs are reviewed employing RFG evaluation of connectivity via asphaltene thermodynamics. RFG processes in reservoris often include diffusion, RFG models incorporating simple solution to the diffusion equation coupled with quasi-equilibrium with the FHZ EoS are shown to apply for timelines up to 50 million years, the age of charge in a reservoir. When gas (or condensates) diffuse into oil, the asphaltenes are destabilized and can convect to the base of the reservoir. Increasing asphaltene onset pressure as well as viscous oil and tar mats can be consequences. Depending on specifics of the process, either gooey tar or coal-like asphaltene deposits can form. In addition, the asphaltene structures illuminated by AFM are now being used to account for interfacial properties using simple thermodynamics. At long last, asphaltenes are no longer the enigmatic component of crude oil, instead the resolution of asphaltene structures and dynamics has led to new thermodynamic applications in reservoirs, the new discipline RFG, and a new understanding of tar mats.

Liners with Bulk Metallic Glass/High Entropy Alloy, Degradable in Formation Fluids for a Skin Free, Clear, Perforating Tunnel, Enabling Enhanced Reservoir Connectivity

A shaped charge for wellbore perforation includes a solid metal or powder liner pressed onto a case, sandwiching high explosives which may have varying thermal stability, dictated by the expected time of exposure and bottom hole temperature (BHT). It is common knowledge that post detonation, the liner-jet punctures the gun body and casing, continuing forward to perforate the formation until its eventual collapse. The jet debris is deposited on the crushed zone forming an impermeable skin and a slug at the end of the perforation-tunnel. This reduces fracture conductivity, and thus, production. Here we present a game changing innovation, the development of a shaped charge with a novel responsive liner. The jet created from our novel degradable liner, post detonation punctures the casing and progress to penetrate the formation until an eventual collapse. However, this system is designed so that, during detonation, a water disintegrable reaction product, bulk metallic glasses (BMG) and/or high entropy alloys (HEA), are formed. These degradable BMG/HEA or complexions decorate the grain boundaries and domain interfaces of the impermeable skin lining the crushed zone of the perforation tunnel as amorphous intergranular films (AIFs) and plug at end of the pathway. Interacting with flowback fluids the BMG/HEA promotes grain dropping, disintegrating the liner and carrot leaving behind a clean perforation tunnel, improving fracture conductivity thus enhanced productivity. In addition, a clear perf tunnel has zero skin value. As such, compared to a coated tunnel with gun and charge debris, it needs little or no acid to clean-up. This results in a demarked reduction of formation breakdown pressures with improved economics for the client. Last but not least this leads to cost reduction of authorized field expenditure (AFE) to support optimized performance of completion design allowing for increased production. CLEAR shaped charges have been qualified to customer specifications in field conditions and are ready to be commercialized. An extension of this technology is being applied to design charges for "Big-Hole" perforations, for the Plug and Abandonment (P&A) market where an effective cement squeeze, anchoring a plug effectively seals the wellbore, preventing the leakage of residual hydrocarbon and associated contamination and emissions.

Powerful Material Technology Removes Barriers

Strengthening materials through grain refinement often results in reduced ductility necessitating means to augment their elongation to failure for engineering applications. Grain boundary engineering (GBE), encompassing novel thermo-mechanical processing has shown promise of simultaneously enhancing both strength and ductility of materials and fracture behavior, especially with low stacking fault energy materials. The ultrahigh strength and reasonable ductility originate from dislocations being effectively blocked at the nano-twinned boundaries resulting in dislocation accumulation and entanglement. This necessitates the careful design of alloys and nano-composites, an effective harnessing of these unique sub-micron features to the benefit of engineering downhole tools for strategic applications. Enabled by these novel material developments, here we present two such articles for the unconventionals. First, a frangible barrier to abet placement of casings and liners through trapping an air column below the barrier while supporting a fluid column in the casing above, providing an up-thrust, a buoyant force that significantly reduces drag and lateral casing weight during placement. This is a viable concept because "shales don't kick". Second is the unmet need for a clean perforating tunnel allowing reduced fluid friction thus better reservoir connectivity. This has been achieved through the development of a novel shape charge with a reactive liner which during the detonation event, additionally generates reactive metallic glassy phase(s) and high entropy alloy complex(s) and their segregation in the deposited jet debris that lines the perf-tunnel. During flowback, reaction with aqueous fluids selectively etch these phases and stimulates the disintegration of the impervious skin on the perf-tunnel into fine particulates subsequently removing them, leaving behind a clear, clean tunnel.

Innovative Use of Injectivity Tests as Interference Tests during Field Development: The EGINA Experience

This paper presents the innovative use of interference tests in the assessment of reservoir connectivity and the field oil production rate during the development phase and prior to the first oil of the EGINA field, which is located in a water depth of 1600 m, deep offshore Niger Delta. The interference test campaign involved 26 pre-first oil wells (13 oil producers and 13 water injectors) to assess and subsequently mitigate reservoir connectivity uncertainties arising from the numerous faults and between the different channels within the complexes. The results proved valuable in confirming or otherwise reservoir connectivity, field oil production rate and the number of wells required at first oil to achieve the production plateau. The tests were designed using the analytical method (PIE software) and the reservoir simulation models enabling to establish the cumulative water injection required, the injection duration and the time a response is expected at the observers. These all had impacts on the planning, OIMR vessel requirements and selection of permanent downhole gauges for the wells. In addition, the tests were performed with the water injectors as pulsers and the oil producers as observers allowing to avoid and the associated environmental impact. Ten interference tests were realized compared to four planned in the FDP partly due to the use of the more cost effective OIMR vessel in addition to the rig.

A Case Study of Complex Carbonate Reservoir Connectivity Analysis, Tarim Basin, China

The connectivity of complex carbonate reservoirs has an essential impact on the exploration and development of these reservoirs. From geological genesis, the connectivity of complex carbonate reservoirs is mainly controlled by faults and dissolution. Therefore, accurate identification of faults and karst caves is the key to studying reservoir connectivity. The Ordovician carbonate reservoir in the Hudson Oilfield of the Tarim Basin is used for the reservoir connectivity analysis study. Firstly, we calculate the coherence and curvature attributes and then merge the two attributes using a neural network algorithm. Finally, we use the ant tracking method to track the faults for the merged data. The results show that the approach substantially enhances deterministic faults that can be seen directly on the seismic data, and the subtle faults can also be identified. For reservoir identification, we use the diffraction imaging method to describe the karst reservoir in this study area. The results show that diffraction imaging can identify small-scale caves that cannot be well recognized on the seismic reflection data. Furthermore, the caves connected on the diffraction seismic data are isolated from each other on the seismic reflection data, making the connection between caves clearer. Based on the results of faults and caves identification, we analyze the reservoir connectivity of the study area using the oil pressure and daily production data. It indicates that the NNW and near-NS faults probably play a role in the connection of the reservoirs, while the NEE faults tend to block the connection of the reservoirs.

Low Well Cost: Effective Cost Optimisation for Marginal Green Field Development Using Fit-for-Purpose Well Design

During the low oil price era, the ability to deliver a small business investment yet high monetary gains was the epitome of success. A marginal field with its recent success of appraisal drilling which tested 3000bopd will add monetary value if it is commercialized as early as possible. However, given its marginal Stock Tank Oil Initially in Place (STOIIP), the plan to develop this field become a real challenge to the team to find a fit-for-purpose investment to maximize the project value. Luxuries such as sand control, artificial lift and frequent well intervention need to be considered for the most cost-effective measures throughout the life of field ‘Xion’. During field development study, several development strategies were proposed to overcome the given challenges such as uncertainty of reservoir connectivity, no gas lift supply, limited footprint to cater surface equipment and potential sand production. Oriented perforation, Insitu Gas Lift (IGL), Pressure Downhole Gauge (PDG), Critical Drawdown Pressure (CDP) monitoring is among the approaches used to manage the field challenges will be discussed in this paper. Since there are only two wells required to develop this field, a minimum intervention well is the best option to improve the project economics. This paper will discuss the method chosen to optimize the well and completion strategy cost so that it can overcome the challenges mentioned above in the most cost-effective approach. Artificial lift will utilize the shallower gas reservoirs through IGL in comparison to conventional gas lift. Sand Production monitoring will utilize the PDG by monitoring the CDP. The perforation strategy will employ the oriented perforation to reduce the sand free drawdown limit compare to the full perforation strategy. The strategy to monitor production through PDG will also reduce the number of interventions to acquire pressure data in establishing reservoir connectivity for the second phase development through secondary recovery and reservoir pressure maintenance plan. This paper will also explain the innovative approaches adopted for this early monetization and fast track project which is only completed within 4 months. This paper will give merit to petroleum engineers and well completion engineers involved in the development of marginal fields.