Understanding reservoir engineering aspects of shale oil development on the Alaska North Slope

Thesis (M.S.) University of Alaska Fairbanks, 2014Horizontal drilling and multi-stage hydraulic fracturing have made the commercial development of nano-darcy shale resources a success. The Shublik shale, a major source rock for hydrocarbon accumulations on the North Slope of Alaska, has huge potential for oil and gas production, with an estimated 463 million barrels of technically recoverable oil. This thesis presents a workflow for proper modeling of flow simulation in shale wells by incorporating results from hydraulic fracturing software into hydraulic fracture flow modeling. The proposed approach allows us to simulate fracture propagation and leak-off of fracturing fluid during hydraulic fracturing. This process honors the real proppant distribution, horizontal and vertical variable fracture conductivity, and presence of fracturing fluid in the fractures and surrounding matrix. Data from the Eagle Ford Shale in Texas was used for this modeling which is believed to be analogous to Alaska's Shublik shale. The performance of a single hydraulic fracture using a black oil model was simulated. Simulation results showed that for the hydraulically fractured zone, the oil recovery factor is 5.8% over thirty years of production, to an assumed economic rate of 200 STB/day. It was found that ignoring flowback overestimated oil recovery by about 17%. Assuming a constant permeability in the hydraulic fracture plane resulted in overestimation of oil recovery by almost 25%. The conductivity of the unpropped zone affected the recovery factor predictions by as much as 10%. For the case investigated, about 25% of the fracturing fluid was recovered during the first 2 months of production; in total, 44% of it was recovered over thirty years. Permeability anisotropy was found to have a significant effect on the results. These results suggest that assuming a constant conductivity for the fractures and ignoring the presence of water in the fractures and the surrounding matrix leads to overestimation of initial production rates and final recovery factors. In addition, the modified workflow developed here more accurately and seamlessly integrates the modeled induced fracture characteristics in the reservoir simulation of shale resource plays

Improved Design and Analysis of Diagnostic Fracture Injection Tests

Diagnostic Fracture Injection Tests (DFITs) have become commonplace in low-permeability (unconventional) reservoirs to obtain parameters used in hydraulic fracture stimulation design and reservoir characterization including minimum in-situ stress, initial reservoir pressure and reservoir permeability. The current understanding of the parameters that impact successful DFIT design and analysis is limited. A DFIT exhibits very complex physical behavior, with various mechanisms active at the same time, including those related to wellbore, fracture, leakoff and reservoir flow. Therefore, the observed trends in field data are not often predicted using existing analytical methods, and some common signatures cannot be interpreted. This underscores the need for a systematic simulation study of DFIT responses where all the active mechanisms are captured simultaneously. Furthermore, the required shut-in time to acquire reliable DFIT data for estimation of minimum in-situ stress and reservoir pressure may be excessive, ranging from days to weeks or months. In this study, a fit-for-purpose coupled reservoir-geomechanics model is used to simulate DFITs and generate synthetic pressure responses under various conditions. The validity of the simulation model is confirmed by comparison to field data. Progressive fracture closure is presented as an alternative closure mechanism, and the primary pressure derivative (PPD) is identified as a powerful tool to estimate fracture closure. The effect of wellbore storage, leakoff rate and dynamic fracture geometry on pressure response is investigated, and their signatures are identified. These findings are used to explain and analyze field data in major unconventional plays in western Canada. In order to accelerate the test and reduce shut-in time, a new DFIT procedure which combines the injection period with an ultra-low rate flowback is presented. Two successful field trials of this modified procedure are reported in this work. Finally, a conceptual method is presented for estimation of reservoir pressure in pump-in/flowback tests. This method utilizes rate transient analysis techniques to account for variations in pressure and flowback rate. This method is validated with numerical simulation and a field trial

Impact of Age on Survival of Patients with Operable Breast Cancer

Background: Breast cancer arising in young patients (? 40 years) is being considered as a distinct clinical entity with more aggressive tumor features and poorer survival. Our aim was to assess the impact of age on survival among a large group of Iranian women diagnosed with breast cancer. Methods: In a cross-sectional study, demographic and clinicopathological characteristics of patients with breast cancer who were treated in two referral centers in Tehran, Iran during the past 13 years were reviewed and extracted from an electronic database. Patients were divided into two groups based on the age at the time of diagnosis (?40 and >40 years). The association of age with different clinicopathological features and its impact on disease-free survival were assessed. Results: Study population comprised of 353(26.1%) patients who were 40 years old or younger and 1000(73.9%) who were older. Compared to older patients, younger participants had more commonly tumor size larger than 5 cm (P = 0.034), higher chance of lymph node metastasis (P = 0.036), and overexpression of HER-2 (P = 0.004). No significant differences were observed between the two groups regarding ER, PR, and LNR (lymph node ratio). Age was the only factor affecting patients' disease-free survival and younger patients had higher chance of local or distant metastases compared to older subjects (HR: 1.49, 95%CI: 1.02-2.17, P = 0.038). Conclusions: Based on the results of current study, it can be suggested that younger patients who are diagnosed with breast cancer tend to have larger tumor size, higher chance of lymph node metastasis and overexpression of HER-2 compared to patients older than 40 years. Age was the only significant factor that was associated with shorter disease-free survival