PH-induced metal-ligand cross-links inspired by mussel yield self-healing polymer networks with near-covalent elastic moduli.

Operating Oil and Gas wells safely requires two tested and independent barriers are in place at all times. If a barrier is lost, all efforts should be focused on restoring the lost barrier. This requires a detailed risk assessment is carried out and an approved deviation in place. The objective in this case was to ensure the only barrier, kill fluid, is not lost to the formation and ensure zero damage to the reservoir. In this paper, the detailed planning and execution of a well in the Eastern Delta (Ukos-21L) with compromised tree valves due to a blown-up Wireline Retrievable Surface Controlled Sub-Surface Safety Valve (WRSCSSV) that got stuck across the tree valves are presented. With a reservoir pressure of 4,000psi, this posed serious HSE risks. The intervention involved establishing injectivity through the kill wing valve. The well was bull-headed to 0psi with appropriate kill brine. A crosslinked polymer gel was then pumped to prevent fluid loss of the only barrier (kill brine) and to ensure well remained stable at 0psi throughout the barrier restoration One of the key project deliverables was to ensure the reservoir was not impaired and the well productivity unchanged during the barrier restoration activity and this was confirmed after the well was successfully put back to production post restoration operation. The crosslinked gel placed across the perforated interval prevented fluid loss without penetrating the formation but due to the introduction of internal chemical breaker, the uncross-linking of the polymer gel was done in-situ after the specified design period elapsed as determined through laboratory test done based on the formation downhole temperature. The well continued to produce ca.880bopd post the integrity restoration. The restored valves were all operable. It was also observed that the installed WRSCSSV was not dressed with the right size of packings, making it possible for the valve to be blown out of its profile. The use of polymer gel is a safe means of preventing fluid loss under a one barrier condition (fluid barrier). The pre-determined breaking period for the cross-linked polymer gel was considered and very critical to the successful execution of the activity. The execution was achieved four days ahead of the planned time with zero non productive time, NPT recorded. Hence, coiled tubing, CT was deployed to nitrogen lift the well to production post integrity restoration. Production was restored three days ahead of schedule.

Polymer gels are widely used in oil–gas drilling and production engineering for the purposes of conformance control, water shutoff, fracturing, lost circulation control, etc. Here, the progress in research on three kinds of polymer gels, including the in situ crosslinked polymer gel, the pre-crosslinked polymer gel and the physically crosslinked polymer gel, are systematically reviewed in terms of the gel compositions, crosslinking principles and properties. Moreover, the advantages and disadvantages of the three kinds of polymer gels are also comparatively discussed. The types, characteristics and action mechanisms of the polymer gels used in oil-gas drilling and production engineering are systematically analyzed. Depending on the crosslinking mechanism, in situ crosslinked polymer gels can be divided into free-radical-based monomer crosslinked gels, ionic-bond-based metal cross-linked gels and covalent-bond-based organic crosslinked gels. Surface crosslinked polymer gels are divided into two types based on their size and gel particle preparation method, including pre-crosslinked gel particles and polymer gel microspheres. Physically crosslinked polymer gels are mainly divided into hydrogen-bonded gels, hydrophobic association gels and electrostatic interaction gels depending on the application conditions of the oil–gas drilling and production engineering processes. In the field of oil–gas drilling engineering, the polymer gels are mainly used as drilling fluids, plugging agents and lost circulation materials, and polymer gels are an important material that are utilized for profile control, water shutoff, chemical flooding and fracturing. Finally, the research potential of polymer gels in oil–gas drilling and production engineering is proposed. The temperature resistance, salinity resistance, gelation strength and environmental friendliness of polymer gels should be further improved in order to meet the future technical requirements of oil–gas drilling and production.

A simple model has been investigated to elucidate the mean squared displacement (MSD)of probe molecules in cross-linked polymer gels. In the model, we assume that numerouscavities distribute in the inhomogeneous interior of a gel, and probe molecules are confinedwithin these cavities. The individual probe molecules trapped in a gel are treated asBrownian particles confined to a spherical harmonic potential. The harmonic potential ischosen to model the effective potential experienced by the probe particle in the cavityof a gel. Each field strength is corresponding to the characteristic of one typeof effective cavity. Since the statistical distribution of different effective cavitysizes is unknown, several distribution functions are examined. Meanwhile, thecalculated averaged MSDs are compared to the experimental data by Nisato et al (2000Phys. Rev. E 61 2879). We find that the theoretical results of the MSD are sensitive tothe shape of the distribution function. For low cross-linked gels, the best fit isobtained when the interior cavities of a gel follow a bimodal distribution. Such aresult may be attributed to the presence of at least two distinct classes of cavityin gels. For high cross-linked gels, the cavities in the gel can be depicted by asingle-modal uniform distribution function, suggesting that the range of cavity sizesbecomes smaller. These results manifest the voids inside a gel, and the shape ofdistribution functions may provide the insight into the inhomogeneous interior of a gel.

Cross-linked polyacrylamide gel as loss circulation materials for combating lost circulation in high temperature well drilling operation

Edited by P. D. Evans London: Academic Press (2002) 428p. ISBN 012024229X £89.95 hardback. ![Figure][1] Reviews published in Advances in Insect Physiology are typically comprehensive treatments of an area by renowned experts in the field, and volume 29 is no

This work reports design and synthesis of side chain amino acid based cross-linked polymeric gels, able to switch over from organogel to hydrogel by a simple deprotection reaction and showing superabsorbancy in water. Amino acid based methacrylate monomers, tert-butoxycarbonyl (Boc)-l/d-alanine methacryloyloxyethyl ester (Boc-l/d-Ala-HEMA), have been polymerized in the presence of a cross-linker via conventional free radical polymerization (FRP) and the reversible addition-fragmentation chain transfer (RAFT) technique for the synthesis of cross-linked polymer gels. The swelling behaviors of these organogels are investigated in organic solvents, and they behave as superabsorbent materials for organic solvents such as dichloromethane, acetone, tetrahydrofuran, etc. Swollen cross-linked polymer gels release the absorbed organic solvent rapidly. After Boc group deprotection from the pendant alanine moiety, the organogels transform to the hydrogels due to the formation of side chain ammonium (-NH3(+)) groups, and these hydrogels showed a significantly high swelling ratio (∼560 times than their dry volumes) in water. The morphology of organogels and hydrogels is studied by field emission scanning electron microscopy (FE-SEM). Amino acid based cross-linked gels could find applications as absorbents for oil spilled on water as well as superabsorbent hydrogels.

Microencapsulation of 2,2′-Azobis(2-methylpropionamide) dihydrochloride initiator using acrylonitrile butadiene styrene as shell for application in lost-circulation control

We model the behavior of a single colloid embedded in a cross-linked polymer gel, immersed in a viscous background fluid. External fields actuate the particle into a periodic motion, which deforms the embedding matrix and creates a local microcavity, containing the particle and any free volume created by its motion. This cavity exists only as long as the particle is actuated and, when present, reduces the local density of the material, leading to swelling. We show that the model exhibits rich resonance features, but is overall characterized by clear scaling laws at low and high driving frequencies, and a pronounced resonance at intermediate frequencies. Our model predictions suggest that both the magnitude and position of the resonance can be varied by varying the material's elastic modulus or cross-linking density, whereas the local viscosity primarily has a dampening effect. Our work implies appreciable free-volume generation is possible by dispersing a collection of colloids in the medium, even at the level of a simple superposition approximation.

Synthesis of amino acid based covalently cross-linked polymeric gels using tetrakis(hydroxymethyl) phosphonium chloride as a cross-linker

Water production is a serious threat during oil production. Cross-linked polymer gels have been used for water shut-off in petroleum production operations for a long time and have proved to be one of the most effective methods. The organically cross-linked polymer gels have longer gelation times, are more stable, and can be applied at higher temperatures and over a wide pH range, as compared to inorganically cross-linked gels; hence, they are more preferable. The gelled polymer treatments can be applied to both injection and production wells to modify the permeability and alter flow in reservoirs to reduce water production and enhance oil production. The work presented involves the investigations on the performance of a hydroquinone/hexamethylene tetramine cross-linked polyacrylamide system. The study involves the detailed in-situ gelation mechanism of the above system by means of sand pack core flooding. The performance and efficiency of this polymer system in an oil field for enhancing oil recovery applications has been judged from these core flooding experiments.

Cross-linked AIE supramolecular polymer gels were successfully constructed by hierarchical self-assembly.

Physical cues, such as extracellular matrix stiffness, direct cell differentiation and support tissue-specific function. Perturbation of these cues underlies diverse pathologies, including osteoarthritis, cardiovascular disease and cancer. However, the molecular mechanisms that establish tissue-specific material properties and link them to healthy tissue function are unknown. We show that Runx2, a key lineage-specific transcription factor, regulates the material properties of bone matrix through the same transforming growth factor-β (TGFβ)-responsive pathway that controls osteoblast differentiation. Deregulated TGFβ or Runx2 function compromises the distinctly hard cochlear bone matrix and causes hearing loss, as seen in human cleidocranial dysplasia. In Runx2+/⁻ mice, inhibition of TGFβ signalling rescues both the material properties of the defective matrix, and hearing. This study elucidates the unknown cause of hearing loss in cleidocranial dysplasia, and demonstrates that a molecular pathway controlling cell differentiation also defines material properties of extracellular matrix. Furthermore, our results suggest that the careful regulation of these properties is essential for healthy tissue function.

In view of the problems of high permeability, high water cut and high recovery in offshore heterogeneous oil fields, the system including cross-linked polymer gel and flexible microgel gel was prepared indoors, which was used in the experiments of classified combination of waterflooding sweep control technology. The SMG microscopic oil displacement experiment shows that after the SMG system is injected into the model, the speed of the displacement fluid in the large pores decreases and the speed of the small pores increases, thereby effectively improving the oil recovery in the small pores. The long core experiment with multiple pressure points proves that the driving method of that cross-linked polymer gel and flexible microgel gel are alternately injected into core, which can block the dominant channel step by step and start. Then the low permeability area was displaced and the displacement fluid continuously diverted in the core, thus maximizing the purpose of oil recovery. The classification and grading water flooding control technology method provides effective technical support for the optimization of process parameters of offshore oilfield.

This paper discusses the gas shut-off treatments carried out in a fractured carbonate field in north Oman and also describes the good practices and lessons learnt from a number of jobs. In addition to the technical analysis, the paper also addresses the economic value of the campaign. Oil production from this field with complex geology and reservoir mechanism was negatively affected by gas breakthroughs in several wells. The constraints on gas handling capacity resulted in shutting-in a number of high GOR wells. These wells were required to be treated to shut-off source of the gas breakthrough in order to restore oil production. Challenges faced in shutting off these gas zones included: 1) Poor cement bond behind the liner shoe. 2) Massive fractures resulting in loss circulation. 3) Uncertainty with fractures volume estimation. 4) Fracture shut-off in open-hole sections. 5) Treatment execution under sub-hydrostatic conditions. To overcome these challenges a robust chemical shut off methodology had to be innovated. This methodology consisted of the following main pillars: a) Utilize various reservoir diagnostics tools to identify fractures and sources of high GOR. b) Use of flowing cross-linked polymer gel combined with a ringing type of cross-linked polymer gel as a capping fluid. c) Utilize an on-fly mixing system that enables volume and concentration adjustment as plugging progression dictates. d) Utilize matrix diagnostics plot along with modified hall plot in real-time to continually estimate flowing gel volume. e) Deploy a fit-for-purpose gel placement assembly for treatment under Sub-hydrostatic conditions.

The Appalachian Basin is known for producing wells that have extreme longevity to include wells that are still producing after 30 or more years. The last several years, Greene County in Pennsylvania has become an active area. The producers have been drilling the Upper Devonian sandstone at depths of 2500 to 5000 feet. Various formations including the Bradford, Speechley, Balltown, and Fifth Sand are typical in a completion of the wells. The conventional completion method has been to utilize a cross-linked polymer gel system. A newer approach utilizing slickwater technology being used on some shale formations has been modified for use in Greene County. The formations commonly average between 4 to 20 feet of net productive reservoir per zone with 6 to 9 percent porosity, and 50 to 80 percent gas saturation. The formations have been difficult to initiate a fracture. Once a fracture has been initiated, transport of proppant into the zones has also been difficult. Screen-outs have been common in stimulating the tight zones. During the flow-back process of a screened-out zone, probable formation particles were observed accompanying the sand during the latter stages of the flow-back. Analysis of the log and flow-back particles indicated the particles were primarily a siltstone or shaley-sandstone. Potential pay zones that show a siltstone or shaley-sandstone composition were selected and treated with a slickwater pre-pad. The volume of slickwater has been 20 to 30 percent of the total volume of the treatment. The slickwater treatment is being used to connect the minor fingerlike fractures within the zone that show shale characteristics. It is believed that the slickwater treatment extends the total fracture length while stimulating the formation. The minor fractures are believed to contribute substantially to the production within the tight gas sands of the Devonian sandstone. A cross-linked polymer gel used to transport proppant follows the slickwater treatment. The fluid used for proppant transport is guar based. The fluid is chemically enhanced while being pumped down the casing to give higher viscosity and proppant transportability. Proppant loading ranges from 0.5 to 3 pounds proppant added. Early production data is showing an increase in initial well production. The production increases have been sufficient to continue the treatments. The increased initial production helps decrease the time required to see a return on the investment for the producer.