Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

First Advisor

Dongmei Wang

Abstract

In unconventional reservoirs, i.e., shaly or tight sand formations, with low porosity and very low permeability, the oil recovery factor is low hence enhanced oil recovery is important. In the conventional reservoirs, once the primary and secondary stages of recovery are exhausted, about two-thirds of the original oil in place is left behind. Enhanced Oil Recovery aims to recover the remaining oil (Green and Wilhite, 1998). These makes the enhanced oil recovery to be of great importance. Efforts are always in place to see how the system can be improved.

The study was carried out to describe the overview of rock types, depositional environment and diagenetic history of the Dawson Bay Formation, and overview of structural geology of the Dolphin Field by studying the Well logs and Cores from the drilled wells, thin sections and using computer softwares i.e. Neuralog, Petra, Surfer. The petrophysical properties of the formation in the field i.e., rock type, porosity, average permeability, oil saturation, production depth, net thickness, temperature and Oil properties, i.e., API gravity, viscosity, oil composition were determined in the laboratory by experiments including Nuclear Magnetic Resonance (NMR) and careful observations of the well logs, and well logs processing using Neuralog, Petra and Artificial Neural network of Matlab. The validity of Screening Criteria by Taber et al. (1997) which recommends Enhanced Oil Recovery Method(s) for formations based on the petrophysical properties for Dawson Bay Formation in Divide County, North Dakota and the optimal method of Enhanced Oil Recovery for the Dawson Bay Formation in Divide County, North Dakota which has its own distinct petrophysical properties and oil properties at laboratory scale at laboratory scale was investigated by conducting Surfactant and brine concentrations spontaneous imbibition experiments, Carbon Dioxide flooding tests, and Carbon Dioxide ‘Huff n Puff’ simulation tests using Computer Modelling Group (CMG) STARS software.

The result of the study shows that the reservoir rock, predominantly dolomite, slightly limestone, thickens from about 10 ft to about 100 ft. It’s thick at the mid-eastern part of the field and thins sideways. This may likely suggest the topography of the marine environment where the limestone was deposited before it was characterized by diagenesis for hydrocarbon accumulation. The oil producing wells are on Nesson Anticline, the reservoir trap has a structural element. Since no clear closure was seen on the structure of the field, reservoir trap may be attributed to halite plugs in the dolomite rock, making it more stratigraphic than structural. The values of the petrophysical properties of the formation obtained from log analysis deviate from values from core analysis. The correlation value was also too low for a reliable relationship. The correlational coefficient for depth 9917 to 9932 ft with 0.5 ft incremental for Well 12071 is about -0.1932, which shows a poor relationship. Artificial Neutral Network (ANN) was used to establish the relationship which can be used to predict the actual petrophysical properties of the formation in other wells. The EOR screening method from Taber et al. (1997) is to a good extent applicable to the Dawson Bay Formation, Dolphin Field. Surfactant flooding and CO2-EOR methods are applicable to the formation based on experimental results and CO2 numerical simulation. The brine, surfactant and CO2 flooding will improve oil recovery from the formation though in varying degrees. The surfactant gave the highest yield of all from experimental results. The prevailing economics, cost of surface and injection plants, environmental among other considerations will influence the method to be used eventually at a time of execution of EOR operation.

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