Leismer SAGD Optimization in the McMurray Formation

Relative permeability of rock is used to predict the flow of each fluid phase, displacement efficiency and expected recoverable reserves. A relationship graph of relative permeability and water saturation were created using data from the following tables

Using the graph above, irreducible water saturation is 0.15. The relationship of relative permeability and water saturation can help to decide the rock type of the reservoir. Cross point is above 50% indicates that the water-oil system is water-wet rock.

Cross point for gas-oil system is below 50%, which indicates that the rock type is oil-wet.

There are 10 pairs of horizontal producer and injector wells actively operating on pad B08. Steam injection through the producer and injector wells started in September 2013 to allow for the steam circulation. Steam circulation is important to achieve communication between the producer and injector wells. Pad B08 was injected with high flowrates of steam up to 5250 m³/day during the steam circulation days to speed up the start-up process which took 90 days. The average daily rate of produced oil is 1460 m³/day and the peak oil production rate is at 2346 m³/day in March 2015. The water production curve follows the same trend as the steam injection curve except that the water is produced at a lower rate which suggests that difference is condensed water left behind in the reservoir.

The pool was initially pressurized with saturated steam at 5000kPa and 264°C during the first 90 days of steam circulation to speed up the start-up process. After the circulation days, the pressure was artificially maintained at an average pressure of 2600 kPa which corresponds to a saturated temperature 226°C.

The production on pad B08 has a cumulative steam injection of 8.68E6 m³ and 4.07E6 m3 of produced oil resulting in 2.30 steam to oil ratio (SOR). The steam to oil ratio is an indicator of the SAGD operation performance. The higher the SOR ratio, the higher the costs of the steam injections. Pad B08 has been maintaining an average SOR of 2.00 which typifies a very efficient production performance.

GOR is the ratio of the produced gas to the produced oil. The GOR is sensitive to the gas behavior in the reservoir gas and is related to steam injected into the reservoir. The gas volume in pad B08 is considered low resulting in minor influence on the oil viscosity. The GOR was at its highest with a value of 85 m3gas/m3oil due to well operations specific to start up and the small size of the steam chamber. As the steam chamber size progresses and the oil production continues, the gas liberates form the oil causing a gradual increase in the GOR reaching a GOR of 43 m3gas/m3oil recently.

Pad B08 production has a WCT ranging from 62% to 67%. The highest WCT percentage are seen during times of low oil rates which are related to the producer well failures.

The original oil in place (OOIP) is calculated using the volumetric method. The pad dimensions were estimated using geoSCOUT measuring tool whereas the gross oil pay, average porosity and initial oil saturation were obtained from logs. The volumetric method accounts for the oil expansion, however; because there is little solution gas in the pool, it is not expected to have a high oil expansion factor. The Standing correlation was used to calculate for the expansion factor. The resulting OOIP is 5.11E6m3 oil which is half a million lower than the reported value by Cenovus.

Sensitivity analyses were also performed on the NPVs, from which we gather that the Oil Prices have the biggest impact on the economics of the project whereas the OPEX and CAPEX are tied for the smallest impact.

In SAGD wells the casing experiences changing thermal states over the life of the well. Ranging tools are a specialized class of directional drilling tools that provide distance to a nearby well. They are used for SAGD operations to drill parallel well pairs. 

Three casings (surface casing, intermediate casing, and slotted liner) will be laid out. The selection of the casing material will take into consideration the operating environment conditions as well as well as the maximum amount of weight the rig is designed to hoist. J 055 is picked up for surface casing and L 80-1 is chosen for the other two. Another important consideration of the casing is the slots. With well designed slots on casing, the production and injection capacity could be maximized without compromising the mechanical integrity nor the sand control. Practically, this means optimizing the slot size and leaving enough space between each slot and between rows of slots.

For this project, we have decided to use the multi-point steam injection method to minimize the possibility of forming a pressure gradient across the well.

Inflow control devices are well completion technologies deployed along the length of the well-aimed at distributing the inflow evenly along the length of the well. ICDs usually consist of a choke, orifice, or valve that restricts flow and create additional pressure drop across the device to balance or equalize well bore pressure drop to create a more evenly distributed flow profile along the horizontal well. Each ICD can be designed (by adjusting the choke diameter) so that the inflow profile along the well is defined leading to a more uniform flow profile along the well. In this process, the simplest method, which is using pre-configured orifices to control steam flow was used. It is also one of the most economically feasible methods in the industry as it saves costs of using FCDs, which are more advanced methods.

The total steam flowrate of this well-pad consisting of 10 well-pairs is 4000 t/d and for one well-pair, a steam flowrate of 400 t/d is used and distributed evenly among 5 orifices along an 800-meter horizontal well. The steam flowrate from each orifice is kept constant at 80 t/d and for this, each orifice has a slightly different diameter. For example, the very first orifice is kept the smallest to ensure that only 80 t/d was exiting it. The remaining steam is sent to orifice 2 which is slightly bigger than the first to allow 80 t/d of steam to flow through it. Similarly, orifice 3 is kept slightly bigger and orifice 4 is allowed to be the biggest for the remaining steam to flow through it.

To calculate the pressure-drop, Unwin’s Formula was used with values from steam tables, an initial pressure of 2600 kPa, a spacing between each orifice is kept as 175 meters and the diameter was calculated using a trial-and-error method.

According to an environmental perspective, using low bleed (low emission) FCD’s can also help in reducing Greenhouse Gas (GHG) emissions. Usage of standard FCD’s such as pressure controllers, level controllers, transducers, and positioners contribute to higher GHG emissions whereas new and improved low bleed models can help bring these emissions down by almost 80 percent. For example, a standard Fisher 4150 pressure controller emits around 42 standard cubic feet of gas whereas, the low bleed Fisher C1 brings that number down to 6.5 standard cubic feet. The government encourages the application of these devices and for this purpose, the Government has introduced incentives such as the Carbon Offset program which allows producers to make money by reducing their emissions. Using these devices will not only help reduce our emissions, but also help in generating offsets that can bring the carbon tax down. Some examples of low bleed devices are shown below: