## 3 Realization of the Investment Using Horizontal Directional Drilling (HDD)  
The horizontal directional drilling technology has been used in Poland since 1991. The first gas pipeline investment to be realized was the pass under the Vistula River in Wloclawek (pipeline with a diameter of DN 500 and length of 1300 m). The HDI (HDI is an indicator that is the product of the length (m) and diameter (inches) of the constructed pipeline. However, this parameter does not take into account other parameters of the trajectory or of the actual geological conditions) (Hole Difficulty Index), calculated as the product of the diameter of the installed pipe in inches and the length of the drilling in meters, of this project was 37,576. Projects are classified, according to the HDI criterion, as follows: small (up to 5000), medium (5000-10,000), large (10 000-20,000), and very large (>20,000). The length of the drilling in the area of Peciszow was 534 m.  
HDD drilling consists of several stages of works that take place directly one after another. These stages are as follows:  
1. Pilot drilling. The drilling is performed using the drilling rig, drill string, drilling tools, and a navigation system. The circulation system of the drilling fluid is closed. The borings that come out of the borehole, together with the drilling fluid, are separated, the excavated soil is stored behind the separator in waste pits, and the treated liquid is poured into the mixer. Next, the fluid of the appropriate parameters is poured into the buffer, then collected from the buffer and fed by a pump into the drill string and, later, into the drill and the wall of the drilling borehole, supporting the processing of the drilled layer. 2. Drilling diameter expansion. The drilling is widened using expanding tools. The process consists of one or two stages. The diameter of the borehole provides an appropriate safety buffer for the installed carrier pipe. The drilling liquid, together with the excavated waste, is transported from the pipe using a transfer pump through a transfer pipeline to the machinery end, where it is separated. 3. Installation of the carrier pipe. The pipe is placed on rollers, then fastened to a swivel and pulled into the drilling borehole using the drilling rig and the drill string. During the whole installation process, drilling fluid is fed directly into the borehole (Figure 3). The analyzed drilling in Peciszow was conducted using several unconventional technological solutions that were unprecedented in the Polish HDD installations market. The achieved progress in creating the borehole exceeded 2.2 m\({}^{3}\)/h gross drilling time, which should be considered a very good result. During the crossing, a total of 27 thousand m\({}^{3}\) of drilling fluid were pumped into the borehole. It was based on inhibited drilling liquid with a moderate solid fraction content. Low installation forces confirmed the correctness of the applied technological solutions during the creation of the borehole and the adopted pipeline ballasting strategy. Navigation was performed using the Paratrack 2 system, equipped with a pressure measurement module. For the first time in Poland, upon the verification of the geological conditions, the contractor of the works decided to widen the borehole from 12 \(\frac{1}{4}\)\" to 52\" in a single step. The quality of the borehole was confirmed by a calibrating march, conducted with an expanded set of tools. The DN1000 pipeline was installed in the borehole on the 8 th of June, with an average recorded traction force of 350 kN. Drilling fluid should only circulate between the designated spots: input earth tank, output earth tank, flow pipe, fraction separation system tank, and active tank. The sizes of the earth tanks should be suitable for the predicted capacity of the mud pump [35]. The appropriate excavations for drilling fluid should be prepared in advance, and its circulation should be monitored throughout the drilling process.