SECTION 7.0 WATER SOURCE MANAGEMENT TABLE OF CONTENTS

Transcription

1 SECTION 7.0 WATER SOURCE MANAGEMENT TABLE OF CONTENTS PAGE 7.0 WATER SOURCE MANAGEMENT Introduction Dewatering Domestic Water Supply Process Water Supply Excess Process Water Disposal Utility Water Supply Cumulative Water Balance Groundwater Monitoring Literature Cited Table of Contents

2 7.0 WATER SOURCE MANAGEMENT 7.1 Introduction Cenovus TL ULC (Cenovus) strives to maximize the efficient use of water in each in situ project. Water is necessary to project operations and plays an important part in many of the processes (e.g., creating steam) required to produce oil. Water source(s) for industrial purposes and steam make-up water, and locations for wastewater disposal, are determined based on the specifics of each project, including the hydrogeological setting. Due to the presence of the overlying Top Water Zone, it is expected that, during steam assisted gravity drainage (SAGD) operations, the ratio of produced water to steam injection will exceed one. As a result, produced water volumes may exceed (Project) requirements. Produced water is cleaned and softened as described in Volume 1, Section for reuse in the steam generators. Cenovus s source water management approach is to use water from the Middle McMurray Top Water Zone, which directly overlies the bitumen zone. Initial boiler feed water will be sourced from the Top Water Zone via the dewatering process. After initial start-up, produced water from the SAGD process will supply all boiler feed requirements. The use of top water is advantageous because it will not be necessary to divert groundwater from another aquifer. Although non-saline, the groundwater from the Top Water Zone may contain trace levels of organic compounds (e.g., petroleum hydrocarbons and polycyclic aromatic hydrocarbons) and, therefore, would require treatment if used for human consumption. In the Water Conservation and Allocation Guideline for Oilfield Injection (AENV 2006), produced water is listed as one of the alternate water sources to offset or replace strictly non-saline make-up water. As noted, the volume of produced water from the Middle McMurray Top Water Zone will exceed Project requirements. Cenovus proposes to manage the excess top water from the dewatering process via injection into the underlying Lower McMurray water zone. Other water management options are also under consideration (Volume 1, Section ). As described further below, process wastewater from the Project is planned to be injected into the saline Middle Devonian Keg River (Methy) Formation. 7.2 Dewatering For SAGD pads that will be dewatered, the dewatering scheme will be utilized to remove top water prior to implementing SAGD, as described in Volume 1, Section 4.3. In the Proposed Project Area (PPA), 54 pads will require dewatering. The dewatering scheme will involve a combination of water production, water reinjection, and air injection to reduce the water saturation in the Top Water Zone above the SAGD bitumen zone. As described in Volume 1, Section 4.3, the water produced from the dewatering water production wells will be reinjected into the pattern periphery, subject to the rate and volume requirements of the water reinjection wells. The surplus top water not required for reinjection will be sent to the dewatering pipeline network for disposal into the Lower McMurray water zone. The dewatering pipeline Page 7-1

3 network will be operated at a steady pressure, and the surplus water will be withdrawn from the dewatering network at the central processing facility (CPF). The surplus water entering the CPF will be degassed and filtered and sent to storage tanks. From the storage tanks, the process water make-up volumes, when required, will be treated as described in Volume 1, Section , and excess top water will be injected into the Lower McMurray water zone. The surplus water in the storage tanks will be used for the fire water system. Contiguous areas comprising multiple pads will be simultaneously dewatered and maintained as dewatered for the duration of SAGD operations in the underlying bitumen zone, as described in Volume 1, Section 4.3. In general, water reinjection wells will be required on the periphery of the dewatered area. A forecast of dewatering volumes has been prepared for the PPA for the life of the Project (Volume 1, Section ). 7.3 Domestic Water Supply A fresh water supply will be required for domestic use (e.g., safety showers, toilets and sinks). If a suitable Quaternary aquifer is confirmed by drilling (drilling is anticipated to occur in 2013), the well would be located in proximity to the new plant site in Section W4M at an expected peak rate of approximately 190 m 3 /d during the construction phase and approximately 60 m 3 /d during the operations phase. Drilling, testing, reporting, and licensing activities would be carried out before developing the actual fresh water supply, as per Alberta Environment and Water (AENV 2011) requirements. 7.4 Process Water Supply A process water supply is required for steam generation. The source will be the Top Water Zone that directly overlies the bitumen. During the first six months of initial steaming start-up operations, it is estimated that up to 5,000 m 3 /d per phase (10,000 m 3 /d for Phases A and B together) will be required for start-up water. The start-up water will be top water derived from a network of dewatering wells located at various well pads. As described further in Volume 1, Sections 4.3, and 7.2, the dewatering wells will start in advance of SAGD operations. The Water Act application for this diversion is provided in Volume 1, Attachment 2. Once oil and produced water recovery begin, produced water will be treated (as described in Volume 1, Section ) and used for steam generation, and the requirements for make-up water will be reduced to zero. 7.5 Excess Process Water Disposal As discussed in Volume 1, Section 3.4.3, a saline zone was confirmed in the Keg River (Methy) Formation at the W4M well. Under normal operating conditions, the average quantity of wastewater disposed will be up to 6,552 m 3 /d, composed of 4,014 m 3 /d of excess produced water, 2,138 m 3 /d of boiler blowdown water and 400 m 3 /d of regeneration water. Page 7-2

4 The wastewater disposal wells will be applied for through regular licensing processes, and the appropriate regulatory agencies and stakeholders will be contacted and consulted for approval as per the normal drilling process. 7.6 Utility Water Supply Under nominal flow conditions, the utility water requirements for the Project are estimated to be 600 m 3 /d, which will be supplied from the top water dewatering operations. Under start-up conditions, though, this volume would be 2,000 m 3 /d per phase (4,000 m 3 /d for Phases A and B together). The Water Act application for this diversion is provided in Volume 1, Attachment Cumulative Water Balance The Block Flow Diagram (Volume 1, Attachment 5) shows the nominal fluid flow volumes for the plant under full operations. Both the dewatering block flows from the well pads are shown, along with the process make-up water flows and the disposal volumes for both the excess top water from dewatering and the excess process water flows. Under normal operations, no process make-up is needed from the top water dewatering system. 7.8 Groundwater Monitoring Cenovus has developed groundwater monitoring programs for the Project that are designed to meet regulatory requirements and to validate predictions of potential impacts to groundwater quality and/or quantity. In summary, the proposed monitoring programs comprise the following: groundwater monitoring associated with a Groundwater Diversion Licence that would be issued under the Water Act for the use of groundwater for domestic and utility purposes at the plant site. The application process would be as outlined by AENV (2011); groundwater monitoring associated with the CPF in order to address typical requirements in an Environmental Protection and Enhancement Act Approval; and a groundwater management plan that includes a proposed conceptual groundwater monitoring program to meet the requirements in Section 1 (Phase 1 New Projects) of AENV s Draft Guideline: Assessment and Management of Non-saline Groundwater in Direct Contact with Bitumen for In Situ Operations (AENV 2009). The proposed monitoring program will include potential locations for compliance monitoring wells, estimated well completion depths, a list of primary and secondary parameters to be analyzed, and a monitoring schedule. Following discussions with AENV, the approved groundwater monitoring network will be installed. Monitoring data will be evaluated on an ongoing basis (as per the Water Act Licence and Environmental Protection and Enhancement Act Approval conditions) in order to confirm that groundwater level and quality remain within expected values. For the groundwater management plan, this will include development of preliminary site-specific targets and thresholds for key water quality and quantity indicators. Page 7-3

5 7.9 Literature Cited Alberta Environment (AENV) Water Conservation and Allocation Guideline for Oilfield Injection. Alberta Environment. Edmonton, Alberta. Alberta Environment (AENV) DRAFT Guideline: Assessment and Management of Nonsaline Groundwater in Direct Contact with Bitumen for In Situ Operations. Alberta Environment. Edmonton, Alberta. Alberta Environment (AENV) Alberta Environment Guide to Groundwater Authorization. Alberta Environment. Edmonton, Alberta. Page 7-4