Castanhal is an onshore heavy oil field located in Sergipe-Alagoas basin northest of Brazil. It is a shallow unconsolidated sandstone reservoir. It has 75 wells where the average reservoir depth is 350m. The oil has high viscosity ranging from 1000 cp to 9000 cp and API gravity ranging from 10° to 16° API.
In early eighties, a small steam injection project was started in the field, but due to operational problems it was interrupted few years later. In that time the oil low prices make the field be practically abandoned: The production was carried on by very few wells without any fluid injection. In 2003, some successful experiences with frac pack and horizontal wells lead to a renewed interest in the field.
Geological and numerical studies have been accomplished and a permanent temperature monitoring technology was selected to improve the reservoir knowledge and validate the studies.
Among the monitoring technologies available in the market DTS (Distributed Temperature Sensing) was selected. It
allows a complete wellbore-temperature profile in few minutes if needed. In this case four observetion wells were equipped with an optical fiber placed along the entire length of the well.
This paper will present a steamflooding pilot in a nine spot, with four temperature observation wells completed with frac
pack to avoid sand production and DTS to improve the understanding of steam breakthrough in the producer wells
and the steam path in the injection well. The information support better decision making to increase steam injection
Castanhal field was discovered in June/1967 by 1-CL-1-SE well. It is located in Brazil and lies on north of the Sergipe-Alagoas basin and It is 50km far from Aracaju city (Figure 1). Its reservoirs are fine-grained sandstones and conglomerates from the Carmopolis Member of the Muribeca Formation, with high permo-porosity, saturated with biodegradeable oil, high viscosity ranging from 1,000 to 9,000 cp and API gravity ranging from 10o API to16oAPI. The oil in place (OIP) is about 178x106 bbl (december/2006).
Figure 1: Castanhal field map location.
The field produced oil by cyclic steam stimulation (CSS) and steamflooding during 1990 year and due to lower Brent prices and high operational costs related to sand face control the steam injection project was abandoned2. In 2001 this situation changed by a well succeded frac pack project with equipaments suited for steam injection. A new steamflooding project in a nine spot was started in june/2006 but now adding distributed temperature monitoring in four observation wells.
The geological interpretation of the well logs in about 73 wells drilled allowed, with confidence, to map four pay zones
MUR/CPS-1, 2, 3 e 4. The Figure 2 shows a well log from Castanhal field with its four zones.
Operationally Castanhal field is divided in four sandstone zones, CPS-1, CPS-2, CPS-3 and CPS-4 with different
geological characteristics. Zone CPS-2 has the best lateral continuity followed by zones CPS-3, CPS-1 and CPS-4, where this last one is more affected by the presence of shales.