A Study of Unconventional Gas Accumulation in Dannevirke Series (Paleogene) Rocks, Canterbury Basin, New Zealand

<p>This thesis aims to assess the potential of unconventional gas accumulation of Danevirke aged (65-43 Ma) mudrock of the Canterbury Basin, South Island, New Zealand. Unconventional hydrocarbon resources contained in low-porosity, low-permeability rocks are potentially a large source of natural gas. Recent developments throughout the United States and increasingly so in Australia, signify a shift in exploration efforts from conventional natural gas targets towards unconventional shale gas plays and basin centred gas systems. Despite extensive international progress made in this field of exploration, little is known about New Zealand unconventional hydrocarbon systems. The Canterbury Basin is approximaty 360,000km² in area and is located approximately between 44°S and 46°S. The deepest part of the basin is located offshore and is known as the Clipper Sub-Basin, which exhibits economic basement depths of 6500m. The Clipper Sub-Basin is a late Cretaceous syn-rift horst and graben feature which trends north east-south west and is bound basinward by the Benreoch High and landward by the Canterbury Bight High. Dannevirke aged transgressive rocks overlay these structures and intermittently exhibit gas-charged intervals in low porosity facies. Elevated gas concentrations are recorded in four exploration wells in the Clipper Sub-Basin from gas chromatograph readings (up to 2 .7/00.4%). These high-gas zones correspond to intervals of elevated quartz (up to 72wt%), whereas non-gaseous intervals corresponded to quartz values as low as 30wt%. Scanning electron microscopy results do not reveal biogenic silica populations in the cutting samples examined. High silica is related to diagenetic silica transformations of mica, various clay minerals, pyrite and silica transformations. Although no visible porosity is observed in thin sections, FMI wireline analysis illustrate natural fractures predominately occur in siliceous intervals, where resistive fractures can account up to one fracture per 10m of stratigraphic thickness. These fissile or laminated brittle lithologies are likely hydrocarbon conduits or accumulation intervals for wet gas. RockEval pyrolysis results indicate the siliceous mudrocks are organic le-n, comprising an immature gas-prone source rock which averages 1.5% total organic carbon. Findings made in this research are compared to the. Whangai Formation, considered in this study to be a comparable shale gas system and also to the Monterey Formation of the United States which is a known basin centred gas system. Dannevirke aged sediments found in the Clipper Sub-Basin appear to constitute the requisites of a near-to-source, direct type., basin centred gas system. Implications of this study open up the possibility that New Zealand's widespread Paleocene-Eocene mudrocks are capable of natural gas accumulation and therefore viable natural gas exploration targets in New Zealand.</p>

A Study of Unconventional Gas Accumulation in Dannevirke Series (Paleogene) Rocks, Canterbury Basin, New Zealand

<p>This thesis aims to assess the potential of unconventional gas accumulation of Danevirke aged (65-43 Ma) mudrock of the Canterbury Basin, South Island, New Zealand. Unconventional hydrocarbon resources contained in low-porosity, low-permeability rocks are potentially a large source of natural gas. Recent developments throughout the United States and increasingly so in Australia, signify a shift in exploration efforts from conventional natural gas targets towards unconventional shale gas plays and basin centred gas systems. Despite extensive international progress made in this field of exploration, little is known about New Zealand unconventional hydrocarbon systems. The Canterbury Basin is approximaty 360,000km² in area and is located approximately between 44°S and 46°S. The deepest part of the basin is located offshore and is known as the Clipper Sub-Basin, which exhibits economic basement depths of 6500m. The Clipper Sub-Basin is a late Cretaceous syn-rift horst and graben feature which trends north east-south west and is bound basinward by the Benreoch High and landward by the Canterbury Bight High. Dannevirke aged transgressive rocks overlay these structures and intermittently exhibit gas-charged intervals in low porosity facies. Elevated gas concentrations are recorded in four exploration wells in the Clipper Sub-Basin from gas chromatograph readings (up to 2 .7/00.4%). These high-gas zones correspond to intervals of elevated quartz (up to 72wt%), whereas non-gaseous intervals corresponded to quartz values as low as 30wt%. Scanning electron microscopy results do not reveal biogenic silica populations in the cutting samples examined. High silica is related to diagenetic silica transformations of mica, various clay minerals, pyrite and silica transformations. Although no visible porosity is observed in thin sections, FMI wireline analysis illustrate natural fractures predominately occur in siliceous intervals, where resistive fractures can account up to one fracture per 10m of stratigraphic thickness. These fissile or laminated brittle lithologies are likely hydrocarbon conduits or accumulation intervals for wet gas. RockEval pyrolysis results indicate the siliceous mudrocks are organic le-n, comprising an immature gas-prone source rock which averages 1.5% total organic carbon. Findings made in this research are compared to the. Whangai Formation, considered in this study to be a comparable shale gas system and also to the Monterey Formation of the United States which is a known basin centred gas system. Dannevirke aged sediments found in the Clipper Sub-Basin appear to constitute the requisites of a near-to-source, direct type., basin centred gas system. Implications of this study open up the possibility that New Zealand's widespread Paleocene-Eocene mudrocks are capable of natural gas accumulation and therefore viable natural gas exploration targets in New Zealand.</p>

Seismic Attribute Analyses and Attenuation Applications for Detecting Gas Hydrate Presence

Identifying gas hydrates in the oceanic subsurface using seismic reflection data supported by the presence of a bottom simulating reflector (BSR) is not an easy task, given the wide range of geophysical methods that have been applied to do so. Though the presence of the BSR is attributed to the attenuation response, as seismic waves transition from hydrate-filled sediment within the gas hydrate stability zone (GHSZ) to free gas-bearing sediment below, few studies have applied a direct attenuation measurement. To improve the detection of gas hydrates and associated features, including the BSR and free gas accumulation beneath the gas hydrates, we apply a recently developed method known as Sparse-Spike Decomposition (SSD) that directly measures attenuation from estimating the quality factor (Q) parameter. In addition to performing attribute analyses using frequency attributes and a spectral decomposition method to improve BSR imaging, using a comprehensive analysis of the three methods, we make several key observations. These include the following: (1) low-frequency shadow zones seem to correlate with large values of attenuation; (2) there is a strong relationship between the amplitude strength of the BSR and the increase of the attenuation response; (3) the resulting interpretation of migration pathways of the free gas using the direct attenuation measurement method; and (4) for the data analyzed, the gas hydrates themselves do not give rise to either impedance or attenuation anomalies that fully differentiate them from nearby non-hydrate zones. From this last observation, we find that, although the SSD method may not directly detect in situ gas hydrates, the same gas hydrates often form an effective seal trapping and deeper free gas accumulation, which can exhibit a large attenuation response, allowing us to infer the likely presence of the overlying hydrates themselves.

Transplastron Enterocentesis to Manage Buoyancy Disorder in an Adult Loggerhead Sea Turtle (Caretta caretta)

Buoyancy disorder in sea turtles is a common condition that contributes to increased morbidity and mortality in the wild and because of this, is often encountered in rehabilitation facilities. The pathological gas accumulation that is a sequelae of this disorder can create challenges in treatment of this disease, especially when concurrent systemic disease is present. These challenges increase with patient size, as anatomy and location of pathology makes gas evacuation more difficult utilizing conventional methods when medical therapy alone is unsuccessful. This report discusses a novel technique utilizing ultrasonic-guided transplastron enterocentesis of the proximal gastrointestinal tract in an adult loggerhead sea turtle ( Caretta caretta ) with suspected intestinal obstruction. The sea turtle presented with positive buoyancy and routine workup revealed gas accumulation in the gastrointestinal tract, as well as concurrent pneumonia. Medical therapy alone did not diminish the positive buoyancy or gastrointestinal distension. Ultrasonic-guided transplastron enterocentesis was performed via the connective tissue lateral to the 3rd inframarginal scute while the turtle was positioned with its left side raised, allowing any gas-filled intestine to be positioned laterally. Approximately 10.3 L of gas were evacuated from the proximal gastrointestinal lumen and within 15 mins, the turtle was neutrally buoyant. It continued to exhibit normal surfacing, diving, and resting behavior. The turtle was released 111 days after enterocentesis in order to allow treatment of the concurrent pneumonia. The technique discussed in this report has implications for improving treatment of buoyancy disorder in large adult sea turtles and increasing likelihood of release.

Study of the dynamics for gas accumulation in the annulus of production wells

Accumulation of associated petroleum gas in the annulus is one of the negative factors that impede the intensification of mechanized oil production. An increase in annular gas pressure causes growth of bottomhole pressure, a decrease in back pressure to the formation and the inflow of formation fluid. In addition, accumulation of gas in the annulus leads to displacement and a decrease in the liquid level above the submersible pump. Insufficient level of the pump submersion (rod or electric submersible) causes a number of complications in the operation of mechanized production units associated with overheating of the elements in pumping units. Therefore, the development of technologies for optimizing the gas pressure in the annulus is relevant. Method for calculating the intensity of gas pressure increase in the annulus of production wells operated by submersible pumps has been developed. Analytical dependence for calculating the time interval of gas accumulation in the annulus, during which the dynamic level decreases to the pump intake, is obtained. This value can be used to estimate the frequency of gas withdrawal from the annulus using compressors. It has been found that the rate of increase in annular gas pressure in time increases non-linearly with a rise in the gas-oil ratio and a decrease in water cut, and also linearly increases with a rise in liquid flow rate. Influence of the operating (gas-oil ratio) and technological (value of the gas pressure maintained in the annulus) factors on the flow rate of the suspended reciprocating compressor driven by the beam engine, designed for forced withdrawal and redirection of the annular gas into the flow line of the well is analyzed.