This paper presents an analytical derivation that constitutes a sound theoretical background for gas flow equation. This gas flow equation is based on a new pseudotime function which, unlike the computation of material balance pseudotime, is insensitive to time step-size and purely analytical. This new pseudotime function offers a simpler approach to handle viscosity-compressibility variations since viscosity-compressibility ratio is a function of cumulative production. Unique to the proposed approach is that the flowing material balance method utilizes pseudocumulative, which is not a function of material balance pseudotime. Currently, the analytical derivation given in the literature for gas flow equation involving material balance pseudotime has created the perception that material balance pseudotime is intuitive. An analytical derivation is given to show that material balance pseudotime function has sound theoretical basis. Presently, iterative scheme, algorithms and graphical techniques involving a number of plotting functions have been proposed to solve gas-in-place. This paper presents a direct approach to solve gas-in-place when early pseudosteady state line is observed. Additionally, a technique is given to validate computed initial-gas-in-place; thus initial-gas-in-place computed by any method can be verified with the proposed technique. The proposed analysis yields initial-gas-in-place, pseudosteady state constant and drainage area. Two simulated and one field published examples are presented to validate our proposed analysis. Introduction Material balance pseudotime has gained widespread acceptance due to its ability to handle general variable pressure/variable rate scenarios. Further, this pseudotime function evaluates variations of gas properties (i.e., viscosity-compressibility values) at average reservoir pressure, and thus, makes it suitable to handle longer-term boundary-dominated flow of real gas. While material balance pseudotime is rigorous for gas wells, it is dependent, as regard its computation, on time step-size. Also, it is not suitable for shut-in periods (Suabdi 2001). Thus, it gives misleading result during shut-in times. Normalized cumulative, has been shown to be a function of material balance pseudotime (Argawal et al 1999; Mattar and Anderson 2003), and thus render its computation time-step-dependent as well.

The focal point of this project is to investigate and assess the potentiality of an enhanced waterflooding process by a naturally generated surfactant (Protein-Enzyme bio-surfactant). The effect of low salinity (LSW), and LSW combined with a bio-surfactant (Protein-Enzyme) in a tertiary mode flooding comparatively. A high salinity water (HS) (0.75 M) was used to flood in the secondary mode after aging the crude saturated core with an initial water saturation of 19%, a recovery of 68.15% oil initially in place (OIIP) was recovered until no further recovery. Upon flooding with a LSW (90% dilution of HS), a further incremental recovery of 11.1% OIIP was produced. Enhancing the LSW with bio-surfactant in a third flooding sequence, an additional 3.75% OIIP was recovered. Analysing the mechanism of LSW bio-surfactant with fractional flow, a high recovery of 0.583 PV (pore volumes) at breakthrough was estimated. Thus, an alteration in ionic strength (salinity) by a 90% dilution and combination of bio-surfactant, saw an incremental recovery, which indicates the potential of LSW bio-surfactant on recovery of residual oil saturation.

The properties of Protein enzyme biosurfactant, a green-enzyme, water-based inert-enzyme generated from the DNA of microbes that eat oil was studied to ascertain its applicability in EOR processes. A light crude oil of 0.908 g/cc at 22°C density and 53.87 cp viscosity was used in this study with a kinematic viscosity which was variable between 90.654 mm2/s to 13.7544 mm2/s between temperatures of 22.5 °C to 70 °C with a measured surface tension of about 35 mN/m. The bio-surfactant yielded a CMC value of 0.02 wt.% which is comparable to reported CMC values of other surfactants. The least IFT value measured was 4.0 mN/m, which is very high for a very efficient and effective residual oil recovery (an ultralow IFT of about 0.01mN/m is required of which was achievable by Rhamnolipid a bio-surfactant studied alongside Protein Enzyme in this work). Ionic (0.083M to 3.0M) and temperature (23 to 70 °C) effects did not have much influence on the activities of bio-surfactant, thus quite stable within such conditions. The protein-enzyme has the ability to form a Winsor type III emulsion and stable over the period of time studied. Adsorption was noticed especially with higher bio-surfactant concentrations but tends to be stable over time.

Due to the ultra-low permeability of unconventional reservoirs, transient state prevails for a considerable period. Despite this, fracture interference can cause an apparent no-flow boundary. Consequently, the Duong's model, which was developed for transient-state period, yields unreliable estimates during the late-time period. In this paper, the Duong's model is modified to account for boundary effects caused by fracture interference and/or unstimulated reservoir regions that serve as no-flow boundaries. Specifically, an empirical correction function, which assumes an exponential decline, has been used as a “modifier” to extend the Duong's model to boundary-dominated flow period. The correction function ensures that during boundary-dominated flow period, an exponential-decline behaviour dominates. The proposed rate-decline model encompasses a gamma function, which converges at large times. Results show that a fractured-well production behaviour is characterised by a decaying power-law during early-time period and tends to exponential decline during late-time period. The results also suggest that although the conventional Duong's model gives good estimates during the transient-state period, it yields optimistic estimates during the boundary-dominated flow period. The proposed model gives a good match and estimates not only in the transient-state period, but also in the boundary-dominated flow period. A major advantage of the proposed model is that it converges to estimated ultimate recovery at large times without imposing any rate and time limits. A good agreement of the estimated ultimate recovery with analytical and semi-analytical models was obtained. Also, results suggest that the proposed model gives conservative estimates. The proposed model will be useful for analysing and predicting both the early- and late-time production performance of a multi-fractured well producing from an unconventional reservoir.