In 2015, Saudi Aramco started a CO2 Water-Alternating-Gas (WAG) EOR pilot project in an onshore carbonate reservoir. To monitor lateral expansion of the CO2 plume, the area was instrumented with a hybrid surface/downhole permanent seismic monitoring system. This system consists of over 1000 buried seismic sensors at a depth of around 70 m, below the the depth of expected weathering layer to mitigate the time-lapse noise. Despite receiver burial, seismic data still suffers from numerous challenges including: significant amounts of high-amplitude coherent noise such as guided waves, mode conversions, and scattered energy; amplitude variations over space and time caused by source and receiver coupling; variability of wavelet shape and arrival times due to seasonal near-surface variations; and low signal-to-noise ratio (SNR). A novel processing workflow was designed for 4D processing of such data. The workflow involves five critical processes. First, the high-amplitude coherent noise is eliminated using FK-based techniques that are 4D compliant to preserve the reservoir changes between repeated seismic surveys. Second, a four-term joint surface-consistent amplitude-scaling algorithm resolves the amplitude variations. The algorithm allows both source and receiver terms to have different scalars for the same positions, but it restricts the other two terms to be position-invariant over different time-lapse surveys, as the window of analysis does not include the reservoir. This is to guarantee that the source and receiver terms are survey-dependent while the other two terms are survey-independent. Thus, the amplitude variability is linked to source and receiver positions over space and time. It also assures that the reservoir changes are not affected by changes in the overburden. Third, wavelet shape variations are addressed using a four-term joint surface-consistent spiking deconvolution algorithm that applies similar principle as the scaling algorithm. Fourth, the small variations in reflection times between different surveys (4D statics) caused by seasonal variations are corrected by a specialized surface-consistent residual statics algorithm using a common pilot derived from the base survey. Fifth, the pre-stack data is supergrouped to enhance the signal-to-noise ratio and repeatability. The processing workflow has been applied to frequent land 3D seismic data acquired over a CO2 WAG EOR pilot project in Saudi Arabia. As a result, we obtained very repeatable seismic images that may successfully detect small CO2-related changes in a stiff carbonate reservoir.

Under the current downturn in the oil and gas industry, the smart design and implementation of state-of-art drilling and completion technologies are key factors toward optimum return on investment. This serves toward authority for expenditure savings, maximum productivity index (PI), and effective operational strategy with minimum risks involved. As part of these efforts, Saudi Aramco successfully deployed the world's longest 4-1/2 in., partially cemented off-bottom liner with a sandstone production equalizer system in an offshore field in Saudi Arabia. This record was achieved through close monitoring of the wellbore condition and accurate torque and drag simulation prior to the job. The 7,389 ft. open hole was horizontally drilled in a 6-1/8 in. section and carefully geosteered through the reservoir to yield a 90% net gross ratio (NGR). As soon as the target depth was reached, a reservoir model was built using the acquired petrophysical and reservoir data, and was employed for design optimization. A hydraulically-set, off-bottom liner system was utilized to spot the ICD screen completion across the desired zones in a single run. The completion liner was designed to provide the appropriate centralization and stiffness, and ensure reaching the borehole bottom. It was challenging to place the well trajectory across the target layer which was just below a gas cap. A reservoir mapping was utilized to better understand the well placement relative to the gas cap. The sandstone production equalizer system and openhole packers were designed to divide the wellbore into sections and balance influx from high and low permeability zones. Restricting flow across the desired sections through introducing higher pressure drops serves into preventing early gas breakthrough from the overlaying gas cap. This achievement was a result of the extensive engineering planning and close operational alertness during sidetracking and deployment. This paper will provide further details on the design and operation phases of this project.