|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Dewatering in Hunton Reservoir - Drill Vertical or Horizontal Well?|
D. Zubarev, SPE, S. Patwardhan, SPE, and M. Kelkar, SPE, U. of Tulsa, and B. Keefer, SPE, Marjo Operating Co.
SPE/DOE Symposium on Improved Oil Recovery, 17-21 April 2004, Tulsa, Oklahoma
2004. Society of Petroleum Engineers
The paper describes an economic analysis carried out for the wells drilled in Hunton Formation in Carney Field in Lincoln County, Oklahoma. The Carney Field produces oil and gas from the Hunton Formation. The field was developed starting in 1995. The Hunton formation covers 2.7 million acres in Oklahoma and in surrounding states of Texas, New Mexico and Arkansas and is one of the most prolific oil producing reservoirs in Oklahoma. Marjo operating Co. is one of the many operators involved in producing from this reservoir. The early development of the Carney field was mostly accomplished through vertical wells. However, in the last two years, the new wells drilled are mostly horizontal wells. It is believed that horizontal wells have better probability of success and better productivity. Horizontal wells also have added advantage of bigger spacing as compared to vertical wells. In this paper, we investigate the efficacy of horizontal wells as against the vertical wells. Our evaluation is based on wells operated by Marjo Operating Company as well as some other operators.
We observe that vertical wells are as economically efficient, or perhaps better, than horizontal wells. We did not find any correlation between horizontal well length and the productivity of the well. Further, for reservoir regions, where the initial oil saturation is higher, vertical wells performed significantly better than horizontal wells.
The West Carney field is located in Lincoln County, Oklahoma as shown in Figure 1. It produces from the Hunton formation. The formation is a highly heterogeneous fractured carbonate reservoir. Initial production from the field was sporadic. The wells drilled early in the life of the field showed excessive water production and were abandoned due to lack of water disposal and surface facilities. Geological studies have confirmed that the reservoir is highly heterogenous and lithofacies vary laterally over short distances.
Although there is some uncertainty regarding the primary mechanism of production, it is believed that the reservoir contains matrix and highly conductive pathways. The reservoir originally contained oil, but the oil was displaced by natural water influx in geological times. At present, oil is largely stored in the matrix and as the water from conductive pathways is produced, oil drains into the pathways and is produced. The reservoir contains light oil; as a result, the production has very high gas oil ratio. The west carney field has been divided into four major regions, which are East, Central East, Central West and West. These regions are based on the geological nature of the reservoir. They are shown in Figure 2.
East and West regions are largely dolomite reservoirs, whereas Central region is primarily made up of fossiliferrous limestone. The initial oil saturations vary greatly over these four regions. The oil saturation in the East region is 0.47, in the Central East region is 0.56, in the Central West region is 0.58 and in the West region is 0.29 respectively. The initial saturation appears to be related to the geological depositional development. Higher dolomatization with higher porosity has resulted in lower oil saturation; whereas, lower porosity in limestone resulted in inefficient water influx development, resulting in higher oil saturation.
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