Utilizing 4D Microgravity To Monitor Water Encroachment

Abstract

The common wisdom is that gravity methods have limited application in the oil industry although they have long been available. The main use of gravity has been for exploration purposes. 4D microgravity monitoring is another new promising gravity application to monitor changes of fluid contacts. Some successful 4D monitoring surveys have been conducted in the industry revealing that this technique is a proven technology in monitoring of gas-water contacts.This paper studies the ability of microgravity to capture movement of the injected water in a giant carbonate field. The oilwater case is more difficult due to the significantly lower density contrast as compared to the gas-water case. Monitoring water floodfront in the field is a key factor in applying successful reservoir management practices to maximize recovery and prolong the field life. The monitoring of inter-well fluids would characterize any pre-mature water breakthrough to allow planning and design of appropriate remedial well interventions. The current applied monitoring tools such as carbon-oxygen and resistivity logs can only detect fluids near to the wellbore due to their shallow radius of investigation. For the study field, 4D seismic cannot be used for fluid movement detection due to issues related to formation acoustics impedance and data quality.The study has shown that surface microgravity monitoring could successfully detect the inter-well fluid changes due to water injection with a high precision tool (0.01 microgal). It also shows that microgravity monitoring can capture water bodies located hundreds of meters away from the location of the 4D measurement.

Reducing Inversion Ambiguity by Use of Reservoir Simulation a Priori Information in Microgravity Oil-Water Flood Front Monitoring

“…7c blue lines) is slightly different from the initial guess (the straight line x ϭ 10,000 m). At the same time, the residual model gravity fit is 0.2 Gal, which is significantly less than the precision of the existing technology surface measurements, as previously discussed, but higher than the tool precision of~0.01 Gal recommended by Alshakhs et al (2008) as the required tool precision to allow a successful inversion of surface gravity data. Subsequently, for some locations, the resulting OWC is distant from the true OWC by more than 500 m. This illustrates that for this example, the uncertainty of the inversion for the location of the OWC from surface data alone is more than 500 m.…”

“…A gravity tool with a very high precision will be required to capture these slight ⌬g changes. Alshakhs et al (2008) generated a synthetic surface microgravity data set by forward modeling using reservoir simulation saturation output. Based on inversion of this synthetic microgravity data, it was concluded that a tool precision of~0.01 Gal is required to be able to successfully detect inter-well fluid substitution changes.…”

“…If the predicted gravity amplitudes are less than the precision of~5 Gal (Alawiyah et al 2012) for the current generation surface gravimeters, it is apparent that gravity monitoring at this time would only be feasible with use of borehole gravity tools and restricted by physical tool size limitations currently imposed on the industry. For example, a gravity monitoring program implementation in the particular oil field presented by Alshakhs et al (2008) would require development of a surface sensor with 0.01 Gal precision to allow successful inversion, or alternatively use workover rigs to temporarily pull the completion out of any near vertical well that was required to be surveyed by borehole tools.…”

“…Lyngra et al (2013) concluded that in one of the producing reservoirs in this field, a heavily fracture dominated reservoir, an improved reservoir simulation model that can be utilized for well placement and oil production predictions can only be constructed by exploiting improved methods to identify fractures and reservoir saturations away from well control. To improve input for the described model and other complex models, seismic, electromagnetic (Marsala et al 2013) and microgravity (Loermans and Kelder 2006;Alshakhs et al 2008) methods are all techniques currently being pursued by Saudi Aramco to improve inter-well fracture characterization and saturation mapping. Nanotechnology saturation mapping options have not been evaluated for this oil field in particular, but a new approach using magnetic nanomappers as a contrast agent for improving deep resolution for electromagnetic surveys (Al-Shehri et al 2013) is currently being investigated in the research laboratory.…”

“…The potential of 4D gravity surveys for inter-well oil/water reservoir surveillance has been evaluated based on modeling feasibility studies. Three of these case studies are using Saudi Arabian field data as input for the microgravity sensitivity cases (Loermans and Kelder 2006;Alshakhs et al 2008;Hadj-Sassi and Donadille 2010). In public domain technical literature, only two successful field applications for using microgravity data for oil field water encroachment monitoring are reported (Alawiyah et al 2012;Hadi et al 2013).…”