Schumi, Bettina (OMV E&P) | Clemens, Torsten (OMV E&P) | Wegner, Jonas (HOT Microfluidics) | Ganzer, Leonhard (Clausthal University of Technology) | Kaiser, Anton (Clariant) | Hincapie, Rafael E. (OMV E&P) | Leitenmüller, Verena (Montan University Leoben)
Chemical Enhanced Oil Recovery leads to substantial incremental costs over waterflooding of oil reservoirs. Reservoirs containing oil with a high Total Acid Number (TAN) could be produced by injection of alkali. Alkali might lead to generation of soaps and emulsify the oil. However, the generated emulsions are not always stable.
Phase experiments are used to determine the initial amount of emulsions generated and their stability if measured over time. Based on the phase experiments, the minimum concentration of alkali can be determined and the concentration of alkali above which no significant increase in formation of initial emulsions is observed.
Micro-model experiments are performed to investigate the effects on pore scale. For injection of alkali into high TAN number oils, mobilization of residual oil after waterflooding is seen. The oil mobilization is due to breaking-up of oil ganglia or movement of elongated ganglia through the porous medium. As the oil is depleting in surface active components, residual oil saturation is left behind either as isolated ganglia or in down-gradient of grains.
Simultaneous injection of alkali and polymers leads to higher incremental oil production in the micro-models owing to larger pressure drops over the oil ganglia and more effective mobilization accordingly.
Core flood tests confirm the micro-model experiments and additional data are derived from these tests. Alkali co-solvent polymer injection leads to the highest incremental oil recovery of the chemical agents which is difficult to differentiate in micro-model experiments. The polymer adsorption is substantially reduced if alkali is injected with polymers compared with polymer injection only. The reason is the effect of the pH on the polymers. As in the micro-models, the incremental oil recovery is also higher for alkali polymer injection than with alkali injection only.
To evaluate the incremental operating costs of the chemical agents, Equivalent Utility Factors (EqUF) are calculated. The EqUF takes the costs of the various chemicals into account. The lowest EqUF and hence lowest chemical incremental OPEX are incurred by injection of Na2CO3, however, the highest incremental recovery factor is seen with alkali co-solvent polymer injection. It should be noted that the incremental oil recovery owing to macroscopic sweep efficiency improvement by polymer needs to be taken into account to assess the efficiency of the chemical agents.
Africa (Sub-Sahara) Algeria awarded four of 31 oil and gas field blocks on offer to foreign consortiums in its first auction since 2011. Shell and Repsol won permits for the Boughezoul area in the north of the country, while Shell and Statoil won permits for the Timissit area in the east. A consortium of Enel and Dragon Oil was awarded permits for both the Tinrhert and the Msari Akabli areas. Circle Oil's CGD-12 well, located onshore Morocco in the Sebou permit, encountered natural gas at different levels within the Guebbas and Hoot sands. Wireline logging analysis confirmed a net 9.7 m of pay. The first test, over the Intra Hoot sands, flowed gas at a sustained rate of 2.21 MMscf/D through an 18/64‑in. The primary target, the Main Hoot sands, flowed at a sustained rate of 4.62 MMscf/D through a 24/64-in.
Africa (Sub-Sahara) Tullow's Cheptuket-1 well in Block 12A of northern Kenya has encountered good oil shows over an almost 2,300‑ft interval, the company reported. The first well to test the Kerio Valley Basin, Cheptuket-1 was drilled to a final depth of 10,114 ft. The results indicate the presence of an active petroleum system with significant oil generation, the company said. Post-well analysis now under way will affect future basin exploration decisions. Tullow is the block operator with a 40% interest. Delonex Energy (40%) and Africa Oil (20%) are the other participants.
Recent drilling results have highlighted the potential for the development of Jurassic source rocks of southern England as a shale oil play. Sustained natural oil flows have been reported by UKOG (2015) from the tight, Lower Kimmeridge limestones in the Horse Hill-1 well. According to the operator, this discovery is naturally fractured and can be produced without hydraulic fracture stimulation.
The occurrence of shale gas in the UK has been known of since the nineteenth century, but development of this resource attracted very little interest until recent years (Selley, 2012; Andrews, 2014). The first exploration well in the United Kingdom that was specifically drilled for shale gas was Preese Hall-1 in northwest England in 2010. This well was hydraulically fractured in the Bowland Shale, but operations were suspended following reports of repeated seismicity caused by the injection of fluid during hydraulic fracture treatment (Green et al., 2012). Assessments of the Carboniferous shale gas potential of northern England and Scotland and of the Jurassic shale oil potential of southern England have been published by the BGS/DECC (Andrews, 2013, 2014; Monaghan, 2014). These studies listed the various criteria for evaluation of shale plays and provided broad descriptions and resource estimates for the Carboniferous and Jurassic shale plays in the United Kingdom.
This paper presents the results of an integrated petrophysical and geological assessment of the Jurassic sequence in the south of England. The study area stretched from the Weald and Vale of Pewsey Basins in the north to the onshore parts of the Portland–Isle of Wight Basin on the Dorset coast in the south (Figure 1). The evaluation focused on the Kimmeridge Clay Formation, the Oxford Clay Formation, the Downcliff Clay Member, Charmouth Mudstone Formation and the Blue Lias Formation.
The stratigraphic framework used for the study is based on the extrapolation of the well-known outcrop stratigraphy on the Dorset Coast to the study wells. Wireline log data and new sedimentological core description results were used to constrain facies mapping. Detailed sedimentological core description was carried out on three of the twelve study wells. From the trends observed in the wireline log data, the lithofacies and level of oxygenation, 14 initial facies associations were assigned over the cored intervals ranging from restricted shallow marine through shoreface to shelfal environments. These facies associations were grouped into seven combined facies associations which were used as input for the electrofacies analysis and facilitated the extrapolation of facies to intervals that lacked core data Additionally this workflow provided a useful template for estimating Total Organic Carbon TOC from logs using the CARBOLOG® equation and this resulted in a significant improvement in the correlation between the laboratory measured TOC values and the log-based TOC estimates. Results from the mineralogical analysis of core and cutting samples were utilised to calibrate and improve the petrophysical interpretations and to assess the elastic properties of the rocks in the intervals of interest. The petrophysical data, elastic properties and the facies interpretations were used to evaluate and map the development potential of the Jurassic source rock intervals as unconventional reservoirs.
An extensive geochemical database was combined with new analyses to characterise the source rocks. This data was integrated into 1-D basin models to identify and map effective source kitchen areas. The organic matter in the analysed interval is dominated by Type II kerogen, with significant input of Type III kerogen towards the London-Brabant Massif. The Upper Jurassic Kimmeridge Clay and the Oxford Clay are within the early oil window, while the Lower Jurassic Downcliff Clay Member, Charmouth Mudstone Formation and the Blue Lias Formation have reached peak oil maturity in the deeper parts of the Weald Basin. The source richness and kerogen types were combined with the maturity maps to create generation risk maps.
The risk for ground water contamination from hydraulic fracturing was also evaluated. These results were combined with the reservoir and generation risk maps to produce common risk segment maps in order to identify the sweet spots in the study area.
Fortenberry, Robert (University of Texas at Austin) | Kim, Do Hoon (University of Texas at Austin) | Nizamidin, Nabijan (University of Texas at Austin) | Adkins, Stephanie (University of Texas at Austin) | Arachchilage, Gayani W. P. Pinnawala (University of Texas at Austin) | Koh, Hee Song (University of Texas at Austin) | Weerasooriya, Upali (University of Texas at Austin) | Pope, Gary A. (University of Texas at Austin)
We have found that the addition of low concentrations of certain inexpensive light cosolvents to alkaline/polymer (AP) solutions dramatically improves the performance of AP corefloods in two important ways. First, the addition of cosolvent promotes the formation of low-viscosity microemulsions rather than viscous macroemulsions. Second, these light cosolvents greatly improve the phase behavior in a way that can be tailored to a particular oil, temperature, and salinity. This new chemical enhanced-oil-recovery (EOR) technology uses polymer for mobility control and has been termed alkali/cosolvent/polymer (ACP) flooding. ACP corefloods perform as well as alkaline/surfactant/polymer (ASP) corefloods while being simpler and more robust. We report 12 successful ACP corefloods using four different crude oils ranging from 12 to 24°API. The ACP process shows special promise for heavy oils, which tend to have large fractions of soap-forming acidic components, but is applicable across a wide range of oil gravity.
Fortenberry, Robert Patton (University of Texas at Austin) | Kim, Do Hoon (University of Texas at Austin) | Nizamidin, Nabijan (University of Texas At Austin) | Adkins, Stephanie (University of Texas At Austin) | Pinnawala Arachchilage, Gayani Wasana Premathi (University of Texas At Austin) | Koh, Hee Song (University of Texas at Austin) | Weerasooriya, Upali Peter (University of Texas At Austin) | Pope, Gary Arnold (University of Texas At Austin)
We have found that the addition of low concentrations of certain inexpensive light co-solvents to alkaline-polymer solutions dramatically improves the performance of alkaline-polymer (AP) corefloods in two important ways. Firstly, addition of cosolvent promotes the formation of low viscosity microemulsions rather than viscous macroemulsions. Secondly, these light co-solvents greatly improve the phase behavior in a way that can be tailored to a particular oil, temperature and salinity. This new chemical EOR technology uses polymer for mobility control and has been termed Alkali-Co-solvent-Polymer (ACP) flooding. ACP corefloods perform as well as ASP corefloods while being simpler and more robust. We report 12 successful ACP corefloods using four different crude oils ranging from 12 to 24 °API. The ACP process shows special promise for heavy oils, which tend to have large fractions of soap-forming acidic components, but is applicable across a wide range of oil gravity.