Tariq, Syed M. (Zakum Development Co.) | Samad, Saleh A. (Abu Dhabi Marine Operating Co.) | Ben Aouda, Abdel Hakim (ZADCO) | Afzal, Muhammad (Zakum Development Co.) | Bengherbia, Mourad (ZADCO) | Graham, Gordon Michael (Scaled Solutions Limited)
A common flow assurance problem during waterflooding operations is the deposition of mineral scale due to mixing of incompatible brines. Deposition of mineral scale can occur anywhere in the production system (reservoir, near wellbore, wellbore, surface facilities) if certain conditions for deposition of scale are present (composition of mixed brine, dynamics of mixing, pressure, temperature and kinetics). Understanding where and how scale will deposit and its impact on production and operations is important especially for the mega offshore field development projects which use new generation of high value wells (long/multi laterals, MRC) associated downhole equipment (ICD, ICV, etc) and surface facilities. In this paper, we present a systematic approach to assessing the scale deposition risk with an example of the application to a giant carbonate field, offshore Abu Dhabi.
Goodwin, Neil (Scaled Solutions Limited) | Svela, Odd Geir (Statoil ASA) | Olsen, John Helge (Statoil ASA) | Hustad, Britt Marie (Statoil ASA) | Tjomsland, Tore (Statoil ASA) | Graham, Gordon Michael (Scaled Solutions Limited)
Method development of laboratory bench and rig tests for assessing the suitability for application of chemicals via down-hole pressure tube systems is presented. Areas of interest include precipitation or viscosity changes due to solvent loss both in bulk samples and samples in capillaries, and long term product stability in capillaries using new flow rigs designed to more fully replicate pressure tube injection phenomena (particularly chemical stability under extreme T and P conditions). Indeed fluid stability and other challenges relating to down-hole continuous injection have led to a number of failures being recorded in recent years indicating that the physical properties rather than the absolute performance of the chemicals is often key to their successful deployment.
Continuous chemical injection systems for down-hole application are being included in more well completions as their usefulness is recognised. While the initial capital costs are increased, such systems provide a number of benefits over reliance on squeeze treatments for down-hole application. These may include the opportunity to use chemicals unsuitable for squeeze treatment due to the risk of formation damage, the ability to maintain higher doses, and avoiding the need to interrupt production to apply chemicals in complex subsea wells.
Using the developed methods we have identified a number of ways in which formulated scale inhibitors may produce problems within continual injection systems. These include particulate formation and line plugging in capillaries, and solid formation or viscosity increases in response to solvent loss within a tube (as opposed to bulk samples).
These methods will form the basis for future qualification procedures for chemicals intended for down-hole chemical injection with the aim of avoiding application issues in the field. They have been developed both to better understand chemical / fluid stability under down-hole continuous injection conditions following a number of recorded field deployment problems, and then to provide improved qualification for new chemicals and systems.
The presence of fractured reservoir zones presents significant challenges for the modelling and optimisation of squeeze treatments. Fluid flow in fractured systems is relatively well understood, and the effect of fractures on the placement of chemical can be modelled. However, to model the quantitative effects of fractures on scale inhibitor returning from squeezed zones, it is necessary to also model the retention and release of inhibitor from a fractured zone. This involves modelling the flow of inhibitor between fracture and matrix, while modelling the retention and release of inhibitor by the rock matrix.
Using conventional near wellbore squeeze simulators (Place iT v5), artificially induced fractures have been simulated using a near wellbore dual permeability approach more commonly used to model wells with a skin factor. The method has been extended from single fractured intervals to dual intervals/zones and the competitive placement of chemical between the fractured zones has been modeled.
The work shows how the predicted chemical placement and the resulting inhibitor return lifetimes can be simulated in fractured wells and how the sizing of the overflush can be more significant than simply accounting for the fracture volume. The mathematical concepts and assumptions used in the model development are presented.
Naturally fractured reservoirs present a special challenge both from the practical scale-management and theoretical (predictive modelling) points of view. Whereas useful conclusions can be drawn using simplified models, more physically meaningful modeling of fracture/matrix interaction is required for the more challenging wells. Rock matrix - fracture interaction can be accounted for using analytical methods including important processes such as molecular diffusion i.e. to account for rock / chemical / fluid imbibition and diffusion. The development of modeling capabilities for such systems is outlined and results from simulations compared with those conducted using more conventional though less rigorous approaches.
Graham, Gordon Michael (Scaled Solutions Limited) | Stalker, Robert (Scaled Solutions Limited) | Wichers Hoeth, Laurien (Scaled Solutions Limited) | Kidd, Samuel Lewis (Scaled Solutions Limited) | Lagarde, Frederic Claude (Total) | Orski, Karine (TOTAL E&P UK PLC)
Coreflood experiments are an integral part of the selection and optimisation of scale inhibitor treatments, providing information on formation damage, inhibitor return profiles and dynamic retention isotherms. However, significant discrepancies can arise between core and field due to test methodology.
In a previous paper (SPE131131), we demonstrated that test methodology can have significant consequences for the comparative inhibitor returns, particularly with respect to oversaturation. The paper showed that many of the limitations can often be overcome through appropriate simulation techniques.
We extend this work and present further results of laboratory core flood tests specifically designed to examine the effect of core flood test methodology on the derived return isotherm, particularly examining the effect of injection of different volumes of main treatment ranging from ~ 0.5 pore volume (under saturated) to 20 pore volumes (over saturated) for a series of different generic scale inhibitors. This work clearly identifies the significant detrimental artefact of inhibitor oversaturation. This paper differs from the previous works (SPE 131131) in that examples are shown where core flood oversaturation can not be overcome with effective isotherm derivation and upscaling. This is due to significant differences in the isotherms derived as a function of the level of oversaturation with main treatment chemical. This paper will also demonstrate the impact of low concentrations of impurities and or the use of chemical blends when testing with poorly designed core flood tests.
Thus the paper directly addresses the procedures involved in core flooding, recommends approaches and test protocols which allow more appropriate product ranking and allow improved simulation from core to field.
Coreflood experiments are an integral part of the selection and optimisation of scale inhibitor treatments, providing information on formation damage, inhibitor return profiles and dynamic retention isotherms. Comparative returns are often used to select the chemical for field treatments. However, significant discrepancies can arise between core and field in particular due to test methodology.
Here we describe advances over previous work when we demonstrated that test methodology can have significant consequences for the comparative inhibitor returns, particularly with respect to oversaturation. It was shown that many of the limitations can be overcome through appropriate simulation techniques (see SPE 131131).
Here, we present the results of laboratory core flood tests designed to examine the effect of core flood test methodology on the derived return isotherm. This work clearly identifies certain test artefacts, in particular inhibitor oversaturation, which can impact simulation from core to field, and presents supportive core flood data with respect to the modelled isotherms. Thus the paper directly addresses the procedures involved in core flooding, recommends approaches and test protocols which allow more appropriate product ranking and allow improved simulation from core to field.