Varun Mishra

Horizontal well drilling is one of the primary technologies unlocking the potential that unconventional reservoirs have provided the industry. However, the advantage of added reservoir exposure is trumped by the difficulty for intervention. Logging operations in shale wells are particularly difficult, due to complex well profiles typically including high dogleg severity and resulting in conveyance and centralization issues, even in horizontal intervals.

Many regulatory agencies now… Show more

Horizontal well drilling is one of the primary technologies unlocking the potential that unconventional reservoirs have provided the industry. However, the advantage of added reservoir exposure is trumped by the difficulty for intervention. Logging operations in shale wells are particularly difficult, due to complex well profiles typically including high dogleg severity and resulting in conveyance and centralization issues, even in horizontal intervals.

Many regulatory agencies now require cement bond logs as evidence for proper zonal isolation in these types of wells. Traditionally, wire line-conveyed logging has been hampered by the inability to access high-angle and horizontal portions of the wellbore and as such, has only been able to quantify cement bond conditions in vertical and low-angle well intervals. The following case study describes the use of a novel centralization method combined with tractor-conveyance to successfully acquire cement integrity data in horizontal wells.

Two successful logging jobs were performed in Marcellus shale (Washington County, PA) wells for Rice Energy, a local operator seeking to verify improved zonal isolation during the multi-stage fracturing process of the horizontal intervals.

The available mono-conductor string (ultrasonic scanning tool, cement bond log tool) operated seamlessly when run with a third-party logging tractor, while complying with operational requirements for pressure control. The inclusion of various concentric centralizer assemblies aided in maintaining ideal centralization and reducing conveyance-related friction to ensure log quality.

The client was not only able to acquire zonal isolation data, but was also very satisfied with log quality that could positively identify cement integrity in both horizontal sections. The use of conventional equipment with an “out-of-the-box” approach solved one of the most complicated challenges with horizontal well intervention. Show less

Abstract
In several places around the world, notably the North Sea and the Middle East, carbonate reservoirs are being accessed with very long horizontal wells (2000 to 20,000 feet of reservoir section.) These wells are often acid stimulated to remove drilling fluid filter cakes and to overcome formation damage effects, or to create acid fractures or deep matrix stimulation to enhance productivity. Good acid coverage with a relatively small acid volume is required to economically obtain the… Show more

Abstract
In several places around the world, notably the North Sea and the Middle East, carbonate reservoirs are being accessed with very long horizontal wells (2000 to 20,000 feet of reservoir section.) These wells are often acid stimulated to remove drilling fluid filter cakes and to overcome formation damage effects, or to create acid fractures or deep matrix stimulation to enhance productivity. Good acid coverage with a relatively small acid volume is required to economically obtain the desired broad reservoir access.

We have developed a model to predict the placement of injected acid in a long horizontal well, and to predict the subsequent effect of the acid in creating wormholes, overcoming damage effects, and stimulating productivity. The model tracks the interface between the acid and the completion fluid in the wellbore, models transient flow in the reservoir during acid injection, considers frictional effects in the tubulars, and predicts the depth of penetration of acid as a function of the acid volume and injection rate at all locations along the completion.

We have used this model to simulate treatments that are typical of those performed in the North Sea and in the Middle East. We present a hypothetical example of acid placement in a long horizontal section and an example of using the model to history match actual treatment data from a North Sea chalk well. Show less