Alberto Marsala

Crosswell Electromagnetic Tomography: from Resistivity Mapping to Interwell Fluid Distribution

A crosswell electromagnetic (EM) technology trial project has been conducted in Haradh field in Saudi Arabia, located in the southern part of Ghawar field. The project objective is to map the fluid distribution and monitor the movement of injected water. Crosswell EM resistivity is one of the technologies that can be deployed for deep reservoir surveillance during hydrocarbon production.

Fluid Distribution Inter-Well Mapping in Multiple Reservoirs by Innovative Borehole to Surface Electromagnetic: Survey Design and Field Acquisition

Borehole to Surface Electromagnetic (BSEM) technology was conceived in the former Soviet Union and fine-tuned by the Chinese Bureau of Geophysical Prospecting (BGP). Saudi Aramco recently deployed the first BSEM pilot test outside of China (Marsala et al., 2011). This paper describes a new world first innovative electromagnetic borehole to surface survey in a well completed with multiple casings. The objective was to deploy a single BSEM survey to map the oil-water distributions in two separate reservoirs. This BSEM survey was conducted in a mature Saudi Arabian oil field composed of two main naturally fractured carbonate reservoirs, separated by a thick nonpermeable zone. The Upper reservoir is prolific, while the Lower reservoir is relatively tight and highly fractured. The reservoir pressure data from the early production period confirmed communication between the two reservoirs through several large scale fractures crossing the nonpermeable zone. In the Lower reservoir, well log observations show a variable oil-water distribution. No direct measurements of fluid saturations are available in the inter-well areas. The BSEM survey was designed to fill this data gap. In June 2012, a very challenging BSEM field acquisition was successfully completed with zero downtime and no accidents, obtaining very good data quality. Electromagnetic (EM) signals were transmitted at multiple frequencies from four source locations placed in a single vertical transmitting well that cross through both reservoirs and received by more than 1,000 surface stations, located in a grid at distances up to 3.5 kilometers away from the transmitting well. Multidisciplinary teamwork and independent peer reviews are undertaken to guarantee the optimal benefit from this pioneering technology. The business impact is to increase recovery by maximizing sweep efficiency and optimize well placements.

Crosswell Electromagnetic Tomography in Haradh Field: Modeling to Measurements

Crosswell electromagnetic (EM) resistivity is emerging as an intriguing technology for reservoir surveillance. It provides a cross-sectional resistivity image between two wells and has the potential to provide fluid distribution at an interwell scale. It can be used for identifying bypassed hydrocarbons, monitoring macroscopic sweep efficiency, planning infill drilling, and improving effectiveness of reservoir simulation. It can be deployed for one-time or time-lapse surveys. A crosswell EM technology trial project is being conducted in an Upper Jurassic carbonate reservoir, at the Ghawar field in Saudi Arabia, to monitor the movement of injected water flood front and map the fluid distribution. The project site is in Ghawar’s southern region, Haradh field, and consists of three wells in the oil-water contact zone where peripheral injection water may have produced an uneven flood front distribution. Significant drilling and well deepening were required prior to the deployment of tools in the three-well triangle. In fact, one new well was drilled and two other wells were deepened by more than 200 m, so that good volumetric coverage could be obtained at the oil-water contact zone. Extensive logs, core and formation tests were also acquired to provide deterministic saturation profiles at the near wellbore region. Formation evaluation in the project area indicates that one of the wells was fully swept while a second well, some 400 m away, was not. In July 2007, crosswell EM surveys were acquired across the three Haradh wells. In spite of the large well separations, the acquired EM data had good quality, and good stations repeatability. Preliminary processing has revealed a structure consistent with the background structure but a clear image of the oil-water contact is yet

Collaborative Development of a Slim LWD NMR Tool: From Concept to Field Testing

ABSTRACT Nuclear Magnetic Resonance (NMR) was identified as a critical technology for reducing uncertainty and minimizing risk during the planning phase of a major field development project. The reservoirs in the subject field contain heavy oil/tar in the flanks, a nd accurate knowledge of viscosity trends becomes essential for the placement of water injectors. Since NMR logs can be used to estimate heavy oil viscosity, the development plan required running logging while drilling (LWD) NMR logs in the extended -reach horizontal injectors, in addition to some selected producers. A program heavily based on slim hole drilling presented a practical challenge for the execution of the development plan, since at the time no service company offered slim hole LWD NMR services. Considering the business impact of this technology gap, Saudi Aramco decided to collaborate with the service industry to develop LWD NMR technology for hole sizes ranging from 5⅞ ” to 6⅛”. Within a year, a joint project was established with a major technology provider for the development of a slim LWD NMR tool. The fi rst two prototypes were delivered for field testing in less than 18 months. The prototypes have been run in nearly a dozen wells to date and in a variety of environments, including extended-reach wells with high salinity muds. Data obtained from drilling and reaming runs agree very well with those from other porosity tools, including wireline NMR. Furthermore, close coordination and cooperation between the operator and the service provider during testing runs have resulted in significant improvements in downhole firmware, data acquisition modes and signal processing. Two factors weigh heavily for the successful fast delivery of the project goals: clear requirements from the operator, and proven expertise in NMR tool design from the technology provider. Giv en continuing reliable and robust performance from the prototypes, the slim LWD NMR service is expected to be commercially available shortly. In fact, the high level of confidence gained from early field tests has already allowed the use of the data in cri tical well placement decisions in some wells.