Thief zone identification based on transient pressure analysis: a field case study

Abstract

Thief zones are generally a channel with high absolute permeability. However, a not very strict theory analysis shows that neglecting the effect of variant of water saturation on formation of thief zone in mature reservoirs cannot explain some thief zones in mature reservoirs. This paper focuses on the effect of water saturation on thief zone development for wells in mature reservoirs with areal permeability heterogeneity. The water saturation increases in high permeable channel with water passing through, which gradually leads to higher value of water phase relative permeability, and thus leads to higher value of effective permeability kÁk rw in the high permeable channel than that in surrounding reservoir. The gradually increasing difference of effective permeability kÁk rw between permeable channel and surrounding reservoir would be the main reason for formation of thief zones in mature reservoir. The oil-water two-phase numerical model based on PEBI (perpendicular bisection) gridding is used to study effect of variant of water phase saturation on formation of thief zone. We find that relatively small pressure change and not obvious bump in pressure derivative curves during shut-in are indicators of thief zones in mature reservoirs. This finding provides a further understanding for the thief zone development and also gives us a guidance to interpret the buildup pressure data in the mature sandstone reservoirs. A field case study verifies the effectiveness of the new explanation.

Cool deltas: Sedimentological, geomorphological and geophysical characterization of ice‐contact deltas and implications for their reservoir properties (Salpausselkä, Finland)

“…16) (Rust & Romanelli, 1975; Powell, 1990; Russell & Arnott, 2003). High porosity contrasts can lead to generation of ‘thief zones’ which are important when a two‐phase flow (gas–liquid/water–oil) is considered, since they may lead to early water breakthrough in wells and isolation of gas pockets, effectively making production impossible (Li et al ., 2016; Satter & Iqbal, 2016). Glaciotectonic modification due to ice‐margin oscillations may effectively decrease sorting of the ice‐contact slope and therefore reduce porosity/permeability creating a zone of decreased reservoir potential (Fig.…”

Identification method of thief zones in carbonate reservoirs based on the combination of static and dynamic data: A case study from the Cretaceous Mishrif Formation in the H oilfield, Iraq

“…During oil and gas recovery, the zones with relatively high permeability will form low-resistivity seepage channels of fluids, that is, the so-called thief zones (Fu et al, 2019). Thief zones will have high oil recovery rates at the early stage of the exploitation, while they will result in an early water breakthrough and, thereby, lead to a low sweep efficiency at the later stage of water flooding development (Li et al, 2015;Kong et al, 2021). Therefore, it is crucial to identify the thief zones in carbonate reservoirs.…”

Thief zone identification and classification in unconsolidated sandstone reservoirs: A field case study

“…Some studies proposed straightforward calculation for thief zone parameters using injection/production data-based simplified one-dimensional flow models (Zhilin et al 2001;Yuetian et al 2003). Pressure responses of the production and injection wells have also been used to identify and evaluate the thief zones quantitatively via well test (pressure transient) analysis based on solving the transient liquid flow problem analytically (Zhao et al 1994;Feng et al 2013) or numerically (Li et al 2016).…”