Selection of completion works

The completion project is to complete the drilling depth of the whole well required by the design, with the operation team or drilling team as the main body, the relevant technical service team participates together, and the equipment and instruments such as workover rigs or drilling rigs are used to carry out construction according to the completion method determined by the design until the well is handed over.

Completion engineering usually consists of completion preparation, completion operation, logging operation, logging operation, perforation operation, testing operation, fracturing operation, acidification operation, and other operations.

The drilling project mainly includes drilling the production layer, determining the completion method of the bottom well, installing the bottom and wellhead devices, and testing the oil for production.

First, opening the production layer completion is to communicate the oil and gas layer and the wellbore, and provide an oil flow channel to ensure that the oil and gas flow from the formation to the bottom of the well.

Any phenomenon that restricts the flow of oil and gas from around the borehole to the wellbore is called “contamination” or formation damage. The process of drilling through the production layer will cause more or less damage to the oil and gas layer.

Therefore, protecting the oil and gas layer is the primary issue facing completions.

After the completion of the oil and gas well, its bottom structure is not easy to change.

Therefore, according to the specific conditions of the oil and gas layer, we should carefully select a reasonable and effective method for completing the bottom of the well concerning the practical experience of various places.

At present, the commonly used bottom completion methods at home and abroad include open-hole completion, perforated completion, slit-lining completion, and gravel-filling completion.

1. 1. Perforation completion method. That is, drilling through the oil and gas layers, going down into the oil layer casing, and perforating the production layer after cementing, this method uses the most extensive
      1. Casing perforation completion
         Casing perforation completion is to drill through the oil layer until the design well depth, then lower the oil casing to the bottom of the oil layer to inject cement cementing, and finally perforate, the perforation catapults through the oil layer casing, cement ring, and penetrates a certain depth of the oil layer to establish an oil flow channel.

Casing perforation completion can selectively shoot open oil layers with different pressures and different physical properties to avoid interlayer interference, and can also avoid interlayer water, bottom water, and gas ceiling, avoid the collapse of the interlayer, and have the conditions for layered operations such as layered injection, mining, and selective fracturing or acidification.

1. 1. 1. Tailpipe perforation and completion
         Tailpipe perforation completion is after the drill bit is drilled to the top boundary of the oil layer, the technical casing is injected into the cement cementing, and then a small drill bit is used to penetrate the oil layer to the design well depth, and the tailpipe is sent down with a drilling tool and suspended on the technical casing. The overlapping section of the tailpipe and the technical casing is generally not less than 50m. The tailpipe is then cemented and then perforated.

Since the upper layer has been sealed by technical casing before drilling the oil layer, the drilling fluid compatible with the oil layer can be used to drill the oil layer by equilibrium pressure and low equilibrium pressure, which is conducive to protecting the oil layer.

In addition, this completion method can reduce the weight of casing and the amount of cement used in the oil well, thereby reducing the completion cost, and most of the deeper oil and gas wells are completed by this method

2. Open-hole completion method. That is, the casing is cemented to the top of the production layer to produce the completion method of the exposed layer section. This method is mostly used for carbonate rocks, hard sandstones, and oil layers with good cementation and simple layers. The advantage is that the exposed area of the production layer is large, and the resistance of oil and gas flowing into the well is small, but it is not suitable for multi-oil layers with different properties and pressures. According to the time of drilling the production layer and entering the casing, the open-hole completion method is divided into the early open-hole completion method and the later open-hole completion method.
3. Lining pipe completion method. That is, the oil casing is cemented down to the top of the production layer, and then the production layer is drilled and the liner with holes is lowered for production, which has a sand prevention effect.
4. Gravel filling and completion method. Fill the liner and the wall of the well with gravel of a certain size and quantity. For strata with severe cementation loose sand, gravel filling, and completion should generally be used.

Completion method selection

Straight well completion method: Straight well completion has a wide range of adaptations, simple process technology, short well construction period, and low cost.

According to the lithology of oil and gas well strata, it can be divided into sandstone, carbonate rock, and other lithology, and these three types of lithology can be completed by straight wells.

In addition, regardless of the type of reservoir in the sandstone reservoir, if it is a low-permeability reservoir, fracturing and production enhancement measures are required; if it is a high-permeability reservoir, the oil layer is loosely cemented and the oil layer is easy to collapse or sand out, sand prevention is required.

Moreover, the thin oil reservoir needs water injection development, the heavy oil reservoir needs steam injection exploitation, and its water absorption, oil recovery, and steam absorption profile should be controlled and adjusted in layers, so it is appropriate to use casing perforation to complete.

As for some single oil layers, there is no air top and bottom water, the permeability of the oil layer is moderate, relying on natural energy exploitation, no fracturing measures to increase production, and it is also feasible to use a lower slit liner to complete wells.

For carbonate reservoirs, if there is no gas top and bottom water in the reservoir, open-hole completions can still be used.

The completion methods of horizontal wells and directional wells can be roughly divided into two categories, the completion method is selected according to the radius of curvature, or the completion method is selected according to the mining method and production increase measures.