Tomographic imaging of residual hydrocarbon in water saturated unconsolidated sediments

Xun Li, Purdue University

Abstract

Determining the amount and distribution of residual hydrocarbon in granular media is important for monitoring secondary and tertiary recovery processes during hydrocarbon production. The distribution of residual hydrocarbon is affected by the structure of the granular media (layering, grain, pore size, etc.), and the method used to produce oil (single well, multi-well, etc.). Seismic technique are often used to monitor the recovery process, thus, it is required that the effect of structure and hydrocarbon distribution be understood. The objectives of this thesis work is to determine if acoustic methods can (1) delineate sediment structure caused by variation in grain size and (2) delineate the amount and spatial distribution of residual hydrocarbon. Naturally occurring sediments are often complicated in composition and structure that results in a range of seismic attenuation mechanisms. For this study, synthetic sediments with idealized 3-D sediment structures were created from glass beads (with known composition and geometry) saturated with two fluid phase: water and paraffin wax. A series of control experiments were performed using different saturation techniques to (1) explore the immiscible fluid displacement processes and (2) to study the effect of amount and the spatial distribution of the immiscible fluid residue on the acoustic response. An acoustic tomographic approach was used to delineate the 3-D sediment structure and to study the effect of sediment structure on the amount and the spatial distribution of the immiscible fluid. From the control experiments, it was determined that the saturation method affected the residual wax distribution in the pores. The residual wax distribution can be categorized into four types, i.e. bridging, thin fingering, cements at grain contacts, and patchy saturation. The tomographic experiments determined that sediment structure caused by a variation in grain size could barely be determined seismically. However, the 3-D sediment structure was clearly determined when residual paraffin resided in the sediment. Even residual saturation of less than 1% altered the seismic signal of the sediments. Seismic-wave attenuation and velocity is sensitive to alteration of the grain contact stiffness even for only a few percent residual hydrocarbon saturation and to spatial features that are ∼1/100 of a wavelength. Thus the affect of micro-scale phenomena on macro-scale measurements of seismic wave attenuation and velocity cannot be ignored.

Degree

Ph.D.

Advisors

Pyrak-Nolte, Purdue University.

Subject Area

Geophysics|Soil sciences

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